The baby, a boy, will join 13-month-old big brother Axel Lee. The couple married in 2008.
"We're having a boy! We're so happy that Axel gets to have a brother so close in age. And that I get to add another set of balls to my very, very male world," the actress, 36, joked to PEOPLE.
For more celebrity pregnancy news, check out Parents.com's 2011 Celebrity BumpWatch.
(image via: http://celebritybabies.people.com)