Osbourne was taping an episode of the E! show "Fashion Police" in front of a studio audience just before noon PST when she told guest host Melissa Rivers, "I don't feel good" -- and then fell to the floor, shaking, TMZ reported.
The report said an audience member, identified as "some kind of emergency responder," tended to Osbourne before an ambulance crew arrived and removed her from the studio on a stretcher -- as people used a sheet to shield her from media.
"She is fine," Joan Rivers told TMZ. "We just saw her."
The report said it was not known what caused the seizure.