The bash was held at the Grand Havana Room, a members-only restaurant and cigar club. After stopping by a party for pal David Arquette's new clothing line, called Propr, Aniston, 39, met up with the group, staying past midnight to ring in Mayer's birthday.
"They seemed to be having a great time," People quoted a source, as saying. "They were sitting next to each other. They're a very good-looking couple and seemed happy together," the source added.
It was their second outing in L.A. this week, following a dinner with friends the night before at the Sunset Towers.