The Revenant star, 41, hit the town in Los Angeles just days after winning a Best Actor trophy at Sunday's Academy Awards, his first after five nominations.
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"Since his Oscar win, Leo keeps celebrating with friends. He has been at several LA clubs since Sunday," the source said. "He has been in the best mood."
"He's usually just cool as a cucumber, he was really chill," former co-star Margot Robbie told PEOPLE earlier this week of DiCaprio's post-win reaction.
Robbie, 25, was more animated.
"I screamed. I literally screamed," she told PEOPLE. "Everyone was beside themselves, no one would sit down, just kept clapping as he was doing his speech. It was an amazing moment."
She wasn't the only one: A Los Angeles street artist celebrated DiCaprio's Oscar with a mural, emblazoned with the words "never never give up."
"We always strive for the best in what we do, but this year in particular, I've been overwhelmed with such support, really truly, by so many fans and so many people in the industry," DiCaprio told reporters immediately after his win. "It's quite shocking honestly, and what can you say but I'm very grateful."