The actress was spotted at LAX on Thursday, Oct. 22, with a small baby bump behind her loose plaid shirtdress.
Byrne, 36, and the Boardwalk Empire actor, 45, began dating in 2012, and have starred on the big screen together in 2014's Adult Beginners and Annie.
The Australian actress was photographed sporting a small baby bump — possibly for her role — while filming Neighbors 2 in Atlanta, Ga., on Thursday, Sept. 10.
The longtime couple kept relatively mum about the relationship during their first year of dating, but began to open up after Cannavale gave Byrne a shout-out during his 2013 Emmys speech.
"And I want to thank the love of my life, Rose," he gushed at the time.
Byrne, meanwhile, dished about her love life in Elle Canada's May 2014 issue. "To be honest, I'm not naturally that much of a romantic person — Australians don't like making a fuss," she said. "I have trouble with things that feel very manufactured, like Valentine's Day. I'm trying to get better at romance."
Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!