While the couple are yet to announce the happy news, model Emma, 35, was seen at a local farmer's market on Sunday with a baby bump clearly visible beneath her pink top.
Bruce, 58, and Emma tied the knot in 2009 and are already proud parents to daughter Mabel Ray, now 20 months.
"I'm happier than I've ever been. I'm changing diapers like a champ," the Red 2 actor told Zoomer earlier this year.
"What I've also discovered is how much love I feel for our baby. I think I'm even more open and more giving as a father now. I pay more attention now because I value it more and I'm less caught up with my career."
The proud star is also dad to daughters Tallulah, 19, Scout, 22, and Rumor, 25, from his previous marriage to Demi Moore.