The former Dawson's Creek star said that he and Brook are delighted to be expanding their family after welcoming their 1-year-old daughter Olivia in September 2010.
He tweeted: "Just when we thought we couldn't feel any more blessed, it seems the universe has plans to give our daughter a sibling..."
The actor previously revealed that becoming a father to Olivia changed the "trajectory" of his life .
Van Der Beek and Brook married last August at a Kabbalah Centre in Tel Aviv, Israel.
He will star in ABC's upcoming midseason comedy Don't Trust the B**** in Apartment 23, which has signed up Thomas Lennon and Bruce Davison for guest roles.
> Dean Cain, Kevin Sorbo for Apartment 23
> James Van Der Beek: 'I'm always mistaken for Mark-Paul Gosselaar'