The US and its allies are closely monitoring Pyongyang for signs of provocation amid a recent escalation of threats from the secretive state, which has warned that it could send Washington a "Christmas gift".
The siren at Camp Casey, which is near the border with North Korea, went off by "human error" at around 10pm on Thursday, said Lt Col Martyn Crighton, a public affairs officer for the 2nd Infantry Division.
The operator immediately identified the mistake and alerted all units at the base of the false alarm, which did not interfere with any operations, Crighton said.
The incident came a day before Japanese broadcaster NHK caused panic by mistakenly sending a news alert saying that North Korea fired a missile over Japan that landed in the sea off the country's northeastern island of Hokkaido early Friday. The broadcaster apologised, saying the alert was for media training purposes.
There are concerns that Pyongyang could react if Washington does not relieve sanctions imposed on the North's broken economy.
North Korea fired two missiles over Japan during a run of weapons tests in 2017, which also included three tests of developmental intercontinental ballistic missiles that demonstrated potential capabilities to reach the US mainland.
Tensions eased after Kim initiated diplomacy with Washington and Seoul in 2018 while looking to leverage his nukes for economic and security benefits.
But negotiations have faltered since a February summit between Mr Kim and Mr Trump broke down after the US side rejected North Korean demands for broad sanctions relief in exchange for a partial surrender of its nuclear capabilities.