The Imagine Dragons front man clearly had a blast onboard a Royal Caribbean cruise from Los Angeles to Los Cabos ... showing off his moves on the dance floor as the DJ played hits from Jay Z and Kanye West, David Guetta and Chris Brown.

As you can see, the dance floor wasn't always packed ... but Dan wasn't shy about cutting a rug. He's mostly dancing by himself, but did find himself in the middle of a circle at one point and appeared to chat up some fans too.

Dan's been the talk of the Internet lately after showing off his muscular body during a recent concert ... and while he sadly doesn't go topless in this portion of the video, you can still see his ripped physique under his tank top.

We're told the cruise set sail Wednesday and Dan tore up the dance floor Thursday night ... but now the ship's coming back to port today after making stops in Ensenada and Cabo.