The NFL superstar is staying busy during his time away from the Steelers ... hitting up Rockwell Nightclub in South Beach to celebrate his "My Side of Things" EP, right after getting in some jet ski cruising earlier in the day.

Not only does the whole club vibe out to his songs, Juice gave a live performance for the crowd (something NFL fans might not see for a while).

Bell -- who seems to be a frequent visitor at Rockwell -- even took a shot at his haters, dedicating his song, "Sayonara," to the people who have been talking about his contract situation.

Safe to assume Bell put on a hell of a show ... the dude even got props from singer/rapper Tory Lanez, who showed Bell some love.