A source confirmed to ABC News that Kiedis was suffering from stomach pains.
The band's gig was part of the KROQ WeenieRoast.
Bassist Flea broke the news to concert-goers about his 53-year-old bandmate's hospitalization.
"Anthony is on his way to the hospital right now and we're unable to play this evening," Flea told concert-goers, as seen in the video below. "We are devastated about it. We're really sad. We love you so much. We live to rock...But unfortunately there's a medical thing that happened and he needed to deal with it."
The band's drummer, Chad Smith, also took to Twitter to wish "a speedy recovery to my brother Anthony."
NO one's more disappointed than us that we couldn't perform tonight. Sending love and a speedy recovery to my brother Anthony. — Chad Smith (@RHCPchad) May 15, 2016