DuBrow (photographed second from left) was 52. The cause of death is not yet known.
"I can't even find words to say," the '80s metal band's drummer, Frankie Banali, wrote on his official Web site. "Please respect my privacy as I mourn the passing and honor the memory of my dearest friends Kevin DuBrow."
Quiet Riot bassist Kelly Garni and the band's current label, Chavis Records, also confirmed the news.
On a Web site honoring the memory of Quiet Riot founding member Randy Rhoads, Garni urged fans to be patient until the details of DuBrow's death become clear.
"I ask that no one here offer any speculation or opinions, theories or other things that could be construed as negative or, and I'm sorry for this, even sympathetic, right at this immediate time," Garni wrote. "I will explain to everyone here the facts and the truth in the next 24 to 48 hours as I realize this will affect us all."
Quiet Riot's biggest hit was "Cum On Feel the Noize," from their breakout 1983 album Metal Health. Their most recent album, Rehab, was released in 2006.