The `Fight Club` hunk joined the former `Friends` actress - best friend of his ex-wife Jennifer Aniston - and 12 other people for their manager, Cynthia Pett-Dante`s, birthday at Beso restaurant in Hollywood.
Despite Brad and Jennifer splitting in 2005, he and Courteney have maintained a good friendship, and they chatted together throughout the night.
An onlooker told website People.com: "They hugged and kissed when they greeted each other. They talked for a while.
"They were chatting, catching up. They both seemed happy and totally relaxed, very at ease. And they were both smiling the entire time. It didn`t seem awkward at all."
Brad - who is now settled with Angelina Jolie, with whom he raises six children, Maddox, nine, Pax, seven, Zahara, six, Shiloh, four and two-year-old twins Knox and Vivienne - reportedly ate a steak and drank beer at the restaurant before joining other guests at the bar, who described him as "really cool".