The singer posted a cute video of Biel, 36, nodding out in the car as the couple was going out in New York City to celebrate his 38th birthday a day early on Wednesday night.
"Gotta work tomorrow for my bday so wifey really going all out tonight...'' Timberlake joked in the caption.
Timberlake has a performance at Madison Square Garden on Thursday as part of his "Man of the Woods" tour, so the two hit the town a night early.
Timberlake mouths the words "happy birthday to me" in the video and then sings in a funny voice as Biel snaps awake. The "Sinner" star wasn't sleeping, she was just resting her eyes.
"I'm just preparing for our big night out!" she said.
It was the latest cute moment for the couple, who are parents to 3-year-old son Silas.
Timberlake wrote about how they first fell in love in his book, "Hindsight: & All the Things I Can't See in Front of Me." Humor has always been a big component of their relationship since they first met at a party in Hollywood.
"I made some sort of sarcastic comment, really dry,'' he wrote. "Nobody got it except her. She laughed, and I noticed, all of a sudden, and in the way where you wonder if a person's like you, if they have a very dry, dark sense of humor, too."
They also have made sure to make time for one another in the midst of their busy careers. Biel and Silas joined Timberlake on the European leg of his tour this past summer, which included a fun family day in Paris and a romantic date on the banks of the River Seine.
Happy birthday, Justin!