The Brietbart News executive was the keynote speaker for the event at the Anaheim Marriott Hotel.
Demonstrators arrived ahead of Bannon's speech. The groups, called the Resistance, Northridge Indivisible and Indivisible OC 46, joined forces for the rally.
They wanted Bannon to know they reject his "extremist and radical alt-right agenda."
"I think that the GOP is being complicit in their support for Trump and for Bannon, and that even moderate GOP representatives and just regular people, their values aren't being represented any more than mine are," protester Diane Bucka said.
During his speech, Bannon said the Trump coalition united behind his concept of nationalism.
"It's about one thing - are you a citizen of the United States of America?" he said. "As a citizen also, you should have preference for jobs and economic opportunities."
He added that winning elections was the primary objective. Bannon also took on recent Republican critics, such as John McCain and former President George W. Bush.
"There has not been a more destructive presidency than George Bush's," Bannon said.
Many people left impressed and said Republicans can take back California with his ideas on building a coalition of voters, such as former President Barack Obama did during his elections.
Last Saturday, Bannon declared a "season of war against the GOP establishment" and had strong words of disdain for Sen. Bob Corker, who made comments about Trump "paving a way for World War III."
Bannon, who spoke at the Values Voter Summit in Washington, D.C., said Corker shouldn't have mocked and ridiculed the president.
The demonstrators in Anaheim had strong words of their own for Bannon.
"I do not support Trump or any of the people that he works with because I think that he has done nothing for the country except create turmoil. But he keeps saying he's going to do away with a lot of the VA benefits and veterans' benefits of which I rely on," protester Mark Casto said.
The groups said no matter how many people come out to protest, they will not tolerate anything but a peaceful demonstration.
Anaheim police monitored protesters and kept them away from the banquet dinner where Bannon spoke. They were kept to a small area in front of the hotel.