could be gaining back some of the 60-plus pounds she lost after giving birth to daughter Maxwell Drew in May.
Us Weekly reports that the singer and "Fashion Star" mentor is pregnant again.
The magazine quoted a source saying, "It definitely wasn't planned. But yes, Jessica is pregnant again."
Simpson's spokeswoman declined to comment on the report to ABCNews.com.
The baby would be the second for Simpson, 32, and her fiance, pro football player Eric Johnson, 33.
The pop star recently shed more than 60 pounds she gained while pregnant with her daughter through a Weight Watchers-controlled diet and four-times-a-week workout sessions with her trainer.
"In over 20 years, I've never seen as consistent of a weight loss," her trainer Harley Pasternak told Us last month. "Jessica's right where she needs to be."
Simpson's Weight Watchers leader Liz Josefsberg told the magazine, "She's very brave to do this in a healthy, more realistic way."
On the premiere of Katie Couric's talk show in September, Simpson admitted that there was a "lot of pressure" on her to lose weight.
She had a lot of incentive, though. Earlier this year, Simpson signed a reported $3 million contract to be the celebrity face of Weight Watchers.
If she is indeed pregnant, it's unclear how this might this affect her contract with the weight-loss program.
"Any questions related to Jessica's personal life can only be answered by her team," company spokeswoman Stephanie Shulman told ABCNews.com. "We do not disclose financial details about any of our relationships with our ambassadors."