The on-and-off-screen couple partied it up with their friends, which included Katy Perry, at the festival.
Robert, 26, sipped on a Gatorade drink while the group watched Jurassic 5 perform at the festival.
Earlier in the week, Kristen and Rob reportedly celebrated her birthday at Malo Restaurant.
A source shared with People, “They celebrated with Mexican food, beers and margaritas. Kristen was in a great mood. She and Rob seemed great too. They were a bit affectionate, but mostly mingled separately.”