The former O.C. star, who met Christensen on the set of 2008's Jumper, allegedly sparked rumours of a separation when she was spotted without her engagement ring at a party in Los Angeles.
However, her representative has dismissed the speculation, telling the New York Daily News: "The engagement is on. She just doesn't always wear the ring."
The notoriously private couple were reported to have confirmed their engagement back in February, when Bilson was allegedly overheard discussing her ring with a fellow passenger on a flight.