Detective Melissa Mercado -- the NYPD detective who went viral for appearing as a stripper in a raunchy music video -- has been taken off active sex crimes cases pending the results of a police review.

Law enforcement sources confirm to TMZ ... Melissa -- who is known as a good investigator -- isn't catching active cases in the Special Victims Unit, which looks into alleged sex crimes, while under review.

We're told police officials have to determine if she submitted off-duty paperwork ... documents every NYPD officer must file if they're working another job off the clock.

As of now, it's unclear if Melissa violated any NYPD rules and regulations by appearing in the "Doin That" video in a bra and G-string. The New York Post was first to report on the police review of Melissa.

ICYMI ... Melissa went viral after appearing as a stripper in the video by NYC rapper S-Quire -- throwing it back in the club, a VIP room and even appearing on a bed in lingerie.

We spoke with S-Quire and the music video's director Pitch Perfect earlier this week ... and, they say Mercado was referred to them by a casting agency -- and, they swear they had no idea she was a cop.