"They haven't been keeping it private really, she's just been working on her business with her family so she hasn't been around," a source told Us Weekly. "She's expecting very soon."
Caan, 37, told Chelsea Handler in 2013 that he had been dating Byxbee for "a couple years."
"She should get the purple heart because I'm a complete disaster," he said.
Caan plays Danno Williams on CBS' remake of Hawaii Five-0.
2014: The Year in Fashion [PHOTOS]
Polly Bergen, Emmy Award-winning actress, dies