A reception for Romney is being held at the Hotel Sofitel San Francisco Bay, located at 223 Twin Dolphin Drive, according to event organizers. Tickets start at $1,000 per person and go as high as $25,000.
Several activist groups protested outside the 5:30 p.m. reception, including Occupy Redwood City, Raging Grannies and Alliance of Californians for Community Empowerment.
Raging Grannies member Ruth Robertson said her group plans to adopt "billionaire personas" and stand outside the event starting at around 4 p.m. with signs mocking people who are driving in to attend.
Occupy protesters also attended the event.
Romney's chief rival for the Republican presidential nomination will be in the Bay Area on Thursday.
Rick Santorum is scheduled to attend a private fundraising event at the home of Mark and Becky Pine in Alamo, according to his campaign. Tickets range from $125 to $2,500. ABC7 News contributed to this report