NFL commish Roger Goodell tells TMZ Sports ... the NFL is officially looking into the Antonio Brown locker room video incident.
Goodell was leaving a media event for the Los Angeles Chargers when he decided to mingle with the fans ... signing autographs, posing for selfies and even talking a little football.
At one point, Roger asked the crowd who they liked in the Super Bowl ... one fan said, "Not the Patriots!" Someone added, "Cheaters!"
Another fan said, "As long as the Cowboys aren't there" -- Roger smiled at that one.