On Thursday, the duo were spotted at The Hotel Caf supporting soulful pop band The Shadowboxers at their L.A. show.
Sharing sweet kisses in the audience, Biel and Timberlake – who are parents to 1-year-old Silas Randall – “were like two high schoolers,” an onlooker tells PEOPLE. “They were definitely enjoying a night away from the baby.”
On Wednesday, the singer urged his followers on Twitter to check out the show. “GO SEE THEM. You will not be disappointed,” he wrote.
Timberlake – who first mentioned the musicians in late 2013 after they covered “Pusher Love Girl” – also surprised the audience by getting on stage and singing with the band. “Many thanks to @jtimberlake for hopping up last night. Incredible,” The Shadowboxers wrote on Twitter.
It’s also been a busy (and fulfilling!) week for Biel. On Wednesday, the star hosted a Mother’s Day playdate with nonprofit organization Baby2Baby and Tiny Prints at her new restaurant Au Fudge.
“They’re like the same person,” Biel gushed earlier this month about her husband and son. “It’s like a mini version of him They like to sit and watch golf together. The only TV that Silas is allowed to watch is the Golf Channel, which is really funny.”
•Reporting by PATRICK GOMEZ