Pattinson reportedly visited The Deer Lodge in California at the weekend with a group of friends from the UK.
The night out came just under two weeks after it emerged that Pattinson's girlfriend and Twilight co-star Kristen Stewart had cheated on him with Snow White and the Huntsman director Rupert Sanders.
People has now claimed that Pattinson went to the bar to see musicians The Jenks.
"Pattinson came in with a few friends, like three guys," a source said. "There was a big party here already and they came in to hang out with the party. There were two girls that were hanging around him, but not Rob necessarily. He seemed happy, fine."
The insider continued: "He was laughing and smiling most of the time, but he was low-key. He didn't really get up. No dancing or anything. He was totally nice and polite."
Pattinson is "heartbroken and angry" following the news of Stewart's fling and that Stewart has been "crying her eyes out".
Pattinson will soon begin to promote his movie Cosmopolis, with interviews on The Daily Show and Good Morning America lined up for next week.