According to a representative of the venue, the 31-year-old singer-actor was the guest of honour among a group of 20 men who "took over the dance floor table" at Tryst nightclub at the Wynn Las Vegas, Us magazine reported.
Wearing a bow tie and a fedora hat, the "Friends With Benefits" star and his group sipped cocktails and Timberlake's own liquor, 901 Tequila.
The crew danced until the wee hours to the sounds of DJ Spider.
"The group was very polite," the representative said.
Timberlake and his friends were then seen at Surrender Nightclub at Encore and Sinatra Restaurant at the Wynn.
Although Surrender - an outdoor pool venue - was besieged with models, Timberlake "was a good boy," an eyewitness said.
"It was just him and his guys," the eyewitness said.
Timberlake proposed to Biel, 30, in the mountains of Jackson, Wyoming in late December 2011.
