Bilson starred in TV's "The O.C." Christensen is best known for playing a young Darth Vader in the three most recent "Star Wars" flicks.
The stars met while filming the 2008 movie "Jumper" together.
Asked at a movie premiere this week how her wedding plans are going, Bilson showed off her ringless hand and told UsMagazine.com: "No, no plans. ... No nothing."
An insider told the Web site the couple started what they intend to be a monthlong break about two weeks ago. They will decide during that time what to do about their relationship, the source said.