"I'm really excited, super excited," the Canadian actress said.
Polley, 32, is known for her role in 2004's Dawn of the Dead and her other credits include eXistenZ and The Sweet Hereafter. She also received an Oscar nomination for writing the 2006 film Away From Her.
The mom-to-be is also celebrating her recent wedding to David Sandomierski. The pair said "I do" two weeks ago in a small ceremony north of Toronto.
"It was pretty much the best wedding of all time," Polley said. "Lots of great food."