There's a clip of the Chiefs QB doing a post-game interview Sunday with the NFL Network, and as he was sitting down and answering questions seriously with an anchor on-camera -- Jackson popped up right behind him and busted a move ... or two, more like.

It looks like Jackson didn't realize he was interrupting a live shot, because someone off-camera appears to have told him to scram ... which he then did, seeming apologetic and genuinely surprised. Pat, meanwhile, didn't bat an eyelash.

Jackson is a social media star in his own right -- thanks, in part, to being Pat's little bro -- and this is his style ... namely, stealing the spotlight. He's often popping up on video doing wacky stuff ... including crap he probably shouldn't be doing, especially at games.

The roped-off area comes to mind -- as does that epic water pour during last season ... among JM highlights from his young career.