Lil Twist -- Justin Bieber's BFF -- has been named in a battery report ... by a woman who claims the rapper got aggressive with her inside Bieb's Calabasas mansion, TMZ has learned.

Law enforcement sources tell us ... the woman who filed the report claims she was hanging out at Bieber's home around 3:30 AM Thursday morning -- Bieber was NOT there btw -- when she decided it was time to leave.

But as she tried to exit the mansion, the woman claims Twist grabbed her by the arm in a forceful manner -- and tried to prevent her from leaving the home.

We're told the woman drove straight from JB's home to a nearby Sheriff's Department.

Sources say cops are investigating the allegation. 

It's not the first time JB's sidekick has been accused of wrongdoing -- just last month, Twist was arrested for DUI while driving Bieber's famous Fisker Karma.

Story developing ...