His return after less than a week of quarantine may violate guidelines from the Centers for Disease Control and Prevention, although it's unclear because little is known about when he was exposed and how often he has been tested.
The State Department has not responded to several questions on the issue since last week.
It also comes as the agency says it is "regressing" in its COVID-19 safety plans for the Washington, D.C., area, according to an email from a senior State Department official that was obtained by ABC News.
Because of the virus spreading, its capital-area offices returned to stricter COVID regulations, including "maximum" telework, "mission critical movements only," and limits on the "size of gatherings." Less than a week ago, the department hosted a holiday reception where hundreds were invited despite CDC guidelines against large indoor gatherings, although Pompeo didn't attend.
"In accordance with CDC guidelines," Pompeo was in quarantine last Wednesday, according to a State Department spokesperson, who said he was "identified as having come into contact with someone who tested positive for COVID" -- without specifying when or where.
CDC guidelines say that anyone exposed to coronavirus "stay home for 14 days after your last contact with a person who has COVID-19." But that time can be cut down to seven days "after receiving a negative test result (test must occur on day 5 or later).
The State Department has refused to provide any other details, including when Pompeo was exposed or when he's been tested.
Either way, returning to the office on Monday would not seem to meet that seven-day window. The department's public schedule, posted Monday morning, says he "attends meetings and briefings, at the Department of State," which, according to one source, included some in-person meetings with his staff and with foreign ambassadors.
He has more in-person meetings scheduled for Tuesday, according to the second source, including with Israel's ambassador to the U.S.
Last Tuesday, the department hosted a holiday reception for the families of U.S. diplomats serving in unaccompanied posts, where it's too dangerous to bring spouses or children. An annual tradition for the agency, invitations are usually sent to hundreds of people, while far fewer actually attend because of travel.
Despite the pandemic and the increase in cases in the D.C. area, the agency invited hundreds of people, two State Department sources told ABC News earlier this month. Only dozens of people attended, however, and Pompeo himself did not end up delivering remarks despite a scheduled appearance.
A week prior, State's acting chief of protocol, Cam Henderson, hosted a similar reception for foreign ambassadors, their spouses, and other VIP guests at the presidential guesthouse Blair House. A third reception for foreign ambassadors at the department was canceled last Wednesday.
Together, the series of holiday receptions brought a wave of criticism, including from lawmakers and the American Foreign Service Association (AFSA), which called on Pompeo to cancel.
"It reflects this my-way-or-the-highway approach that has defined his leadership at State, and it's emblematic of his unwillingness to listen to his own advisers, to the experts who are saying this just either isn't a good idea or is against the rules," said Brett Bruen, a former State Department official. "His response always seems to default to, 'I don't care.'"
Less than a week after the unaccompanied tour reception, the department announced Monday that it was re-implementing stricter COVID policies after a rise in cases in the D.C. area.
In an email to staff obtained by ABC News, Under Secretary for Management Brian Bulatao said the department is "officially regressing to Phase 1" of its COVID strategy. That means staff travel will be limited to "mission critical movements only," offices are required to allow "maximum telework" possible, and visitors and gatherings are to be restricted.
The reimposed restrictions will last until at least January 18, Bulatao said.
In the last month alone, 10 U.S. embassies or consulates around the world have similarly "regressed" because of spikes in COVID cases in that country, according to Bulatao's note, while 65% are in Phase 2, where small gatherings are permitted and up to 80 percent of employees can return to work in-person.
The department had moved its D.C. area offices to Phase 2 at the end of July despite concern from some officials as well as AFSA about forcing people back to work too soon.