11:48 AM PT -- TMZ Sports contacted the Bastrop County Sheriff's Office and a spokesperson told us there is an active investigation into Brown.
We asked if the investigation centered around the June 2019 incident detailed in Marzette-Sanders' lawsuit, but the rep would not give specifics about the probe.
Oakland Raiders star Trent Brown -- the highest paid lineman in the NFL -- is being sued for allegedly beating the hell out of his girlfriend, who says he's a repeat attacker.
The woman behind the suit is Diorra Marzette-Sanders, who says she has a 9-month-old son with the 26-year-old.