Antonio Brown's got lightning-fast reflexes ... but even that wasn't enough to keep him from getting hit in the head by an errant piece of gym equipment.

The out-of-work NFL star appeared to be working out at his 84/7 training facility in Florida -- pushing big weight on the bench press -- when another piece of gym equipment got loose and crashed down on his head.

It's unclear why the workout machine got loose -- but don't worry, AB didn't appear to be injured.

Just a reminder ... be careful in the gym!!

As for his career, Brown has been training like a maniac and recently told TMZ Sports he plans on meeting with team reps at the NFL Combine in Indianapolis when that event kicks off this weekend.

Of course, Brown has a LOT going on off the field that could prevent teams from pulling the trigger -- including an ongoing battery case, allegations of sexual assault, baby mama issues and a very nasty beef with the Hollywood Police Dept.

We know he can play ... but will a team look past everything else to get him on the field?