"I had a party with my friends and family," Damon tells PEOPLE of the gather Friday. "You know, nothing outrageous."
The actor also clears up speculation that he has signed on to direct a new film written by pals Ben and Casey Affleck.
"He and Casey were going to write this movie and I guess Ben was quoted recently saying that he'd love to have me direct it," Damon said. "There is no script yet."
Damon's next film is 'Hereafter', which opens Oct. 22.