Justin Bieber Performs Unannounced Gig in Los Angeles Park

Justin Bieber's headlined Coachella and performed at the World Cup final this year, and he's on the short list to do the Super Bowl halftime show ... but you'll never guess where he performed this week -- a famous park in Los Angeles!!!

Justin was spotted at L.A.'s MacArthur Park on Tuesday afternoon giving fans a free, impromptu performance.

Thumping on a cajón, Justin sang some of his hits -- including the 2025 banger "Yukon" -- in front of the stunned crowd.

Going the extra mile, the singer even took the time to pose for selfies and meet some of his younger fans.

It's been a fun, low-key September for the singer so far! Less than two weeks ago ... the Biebs rang in his 8th wedding anniversary with wife Hailey Bieber in a super casual way.

The pair -- who share 2-year-old son, Jack Blues -- headed to a bar to shoot some pool.

After their outing, Hailey was quick to admit that their marriage involved "8 years of me being horrendous at playing pool."