Bilson starred in the former hit TV series "The O.C." and in the film "The Last Kiss." Christensen is best known for his portrayal of the young adult version of Anakin Skywalker in the "Star Wars" prequels and for his role in the big-screen drama "Shattered Glass."
The couple will soon be seen in the multi-story movie "New York, I Love You."
"I'm happy and that's all that matters," Bilson told Page Six Magazine. "I have someone really great. Someone who can make me laugh -- that's always what comes first. It's the best to be able to really, like, truly laugh with someone like they're your best friend, you know?"
Asked about her opinion on dating guys she works with, the actress -- who also went out with her "O.C." co-star Adam Brody -- replied: "They say don't date your co-star, but that's who you're around. If you're in an office, and you see someone every day and you click well, you'll start dating. It's the same thing."