Britney Spears was a surprise guest at a fundraiser for autism this Saturday in Los Angeles.

The benefit was to raise money for actress Jenny McCarthy's charity, Generation Rescue, an organization dedicated to autism research.

One guest told US Weekly that Spears, 26, "definitely looked happy" and was "smiling a lot" while sipping wine at her table. Another told People magazine that while Spears stayed close to her assistant, Brett, "she was very into the information" that was being presented. This was the pop star's first public appearance since news of her custody agreement broke last week.

Other stars in attendance included Charlie Sheen and his new bride, Brooke Mueller, as well as Robert Rodriguez and girlfriend, Rose McGowan, who danced all night, according to People.

Helping McCarthy with the event was long-time beau comedian Jim Carrey, who at one point took to the dance floor and challenged another guest to a dance battle.

McCarthy's son, Evan, 5, was diagnosed with autism three years ago but she only revealed his condition last May on The View. She's also recently published a book, Louder Than Words: A Mother's Journey in Healing Autism.