Biel's costume was especially comical since she admitted earlier this week on The Tonight Show Starring Jimmy Fallon that she was never a fan of *NSYNC during the group's heyday in the late 1990s and early 2000s.
"I was just listening to old school stuff," Biel told Fallon, noting that her music preferences leaned more toward the Rent soundtrack and Motown. "I lived under a rock, I wasn't into pop culture music."
Friday's Halloween bash, hosted by Casamigos founders Rande Gerber and Mike Meldman, also attracted such celebrity guests as Gerber's wife Cindy Crawford, Paris Hilton and Real Housewives of Beverly Hills star Lisa Rinna.
Rinna, another standout at the party, dressed as Jennifer Lopez wearing her iconic green Versace dress at the Grammy Awards in 2000.