The "Jumper" co-stars got engaged in December, Bilson's friend told People magazine.
"They're so excited," said the insider. "They're a great couple. Rachel seems thrilled beyond belief."
The friend said the couple hasn't set a wedding date yet and Bilson's publicist told People, "I don't comment on my clients' personal lives."
Christensen's publicist declined to comment on the engagement report.
Bilson appeared on the TV show "The O.C." and in the film "The Last Kiss."
Christensen played young Anakin Skywalker in two "Star Wars" films.