The 16-year-old Bieber won for pop/rock male, breakthrough artist, album and artist of the year in the awards ceremony at Nokia Theatre in Los Angeles, People magazine reported. His "My World 2.0" debuted at No. 1 on the U.S. Billboard 200.
"I can't stop smiling," People magazne quoted Bieber, the youngest person ever to win the top AMA honor, as saying.
R&B star Usher, who Bieber called "not only my mentor but my best friend and my big brother," won awards for male soul/R&B artist and for his album, "Raymond v. Raymond."
Eminem was awarded trophies for male rap/hip-hop artist of the year and for his album "Recovery."
Also reaching the stage to accept awards were Lady Gaga for pop/rock female of the year, The Black Eyed Peas for pop/rock group, Brad Paisley for male country artist, Taylor Swift for female country artist, Lady Antebellum for country group and Carrie Underwood for country album of the year for "Play On."