A family source tells PEOPLE that the couple are living together again in Fox's home with their children – Noah, 3½, and Bodhi, 2 – but that there are no plans to cancel the split.
The New Girl star filed for divorce in August after five years of marriage and 11 years together. According to legal filings, the divorce is still pending. Reps for both stars have not commented.
Fox and Austin Green stepped out together in Los Angeles on Tuesday and appeared to be in good spirits amid news of the new baby.
The actress, 29, debuted her baby bump at CinemaCon in Las Vegas on Monday while promoting Teenage Mutant Ninja Turtles: Out of the Shadows.
While some questioned who the father might be, a source confirmed to PEOPLE that Austin Green is "of course" the father and that the pair "never stopped loving each other and they will never stop being devoted parents to their boys.
The pregnancy came as a surprise for the couple, who are "very excited" and are "continuing to work on their marriage and are living together again," another source said.
"They both love being parents," the source adds.
The exes have remained amicable since announcing their split and have often been spotted together with their two children and have also been seen running errands together without the kids.