Kelly, 34, half of rap duo Kriss Kross, gained fame in the 1990s for hits including "Jump." An autopsy is set for today.
Kelly was found at his home and transported to an Atlanta hospital, where he was pronounced dead. He was lying on the living room couch "unresponsive" with "no life signs," according to E!.
Kelly's uncle, Lamar Williams, said that Kelly had a history of drug abuse, including heroin and cocaine. His mother, Donna Kelly Pratt, said he was nauseated all morning the day he died.
"The information we obtained at the scene leads us to believe it was a possible drug overdose," said Fulton County Police spokeswoman Kay Lester. The team is investigating Kelly's death as a drug overdose unless autopsy results indicate otherwise.