Philipps, 33, is best known for her work on "Dawson's Creek," "Freaks and Geeks" and "Cougar Town." She is married to screenwriter Marc Silverstein, the father of her 4-year-old daughter Birdie Leigh.
Philipps announced her news by posting a photo of a positive pregnancy test on Twitter Monday.
"So this happened ...," she tweeted.
People.com confirmed the actress' pregnancy with her publicist.
The baby's gender and anticipated birth date were not reported.