The Des Moines Register reports that Loc, whose real name is Anthony T. Smith, collapsed after finishing a song during a Saturday night concert in Des Moines.
Three of the newspaper's workers who were at the show said people attended to Loc for several minutes before fans were asked to leave.
Loc's condition wasn't immediately clear Sunday. He wasn't listed publicly as a patient at any Des Moines hospital, and no one answered the phone Sunday morning at the bar that sponsored the concert.
Loc's representative did not immediately respond to phone and email messages Sunday.
It wasn't the rapper's first time collapsing on stage. Loc, who is best known for his 1980s hits "Funky Cold Medina" and "Wild Thing," collapsed and had a seizure during a 2009 concert in Pensacola, Fla. Authorities said he had apparently overheated.
Loc also collapsed in 1995 while attending a Los Angeles Lakers game. The reason he collapsed wasn't given.
Loc has also appeared in a number of television shows and movies, including "Ace Ventura: Pet Detective" with Jim Carrey and "Heat" with Al Pacino. Loc has also been the voice of several animated characters.