A man dressed in what looks like a security uniform was caught masturbating near a Metrorail stop in the city … but we’re told he’s not a transit security guard, even though he looks like one.

Here’s the deal … a video of a man going to town on himself is circulating online right now — capturing this individual in a dark blue shirt under a reflective safety vest doing the deed in full view of anyone walking by.

This prompted many online to identify him as Metrorail guard — a security officer who keeps people at these rail stops safe.

As you can imagine, many were freaked out by this clip … but, it turns out the man in it isn’t a Metrorail employee.

A rep for the Miami-Dade County Department of Transportation and Public Works tells TMZ …  “We can confirm 100% that the individual is not a Miami-Dade Transit security guard nor a department employee in any other capacity. Transit security guards are part of the Allied Universal team and wear brown uniforms and do not use vests.”

Law enforcement sources tell TMZ they’re looking into this incident … but, no official report has been filed, and they haven’t made any arrests yet. It’s unclear when the incident occurred — the video was posted Tuesday.