A potential melee was quelled when police backed down and left the bank being held by 50 or more members of Occupy Santa Cruz.
The Occupiers say they want to make the empty former Coast Commercial Bank, now owned by Wells Fargo, their winter headquarters.
Police spokesman Zach Friend said police left because they were outnumbered and didn't think it was safe.
Earlier, a line of officers tried to keep more people from entering the bank and then tried to enter it themselves, but Occupiers stacked office furniture to block the way.
Two people were arrested early on, said Friend, who didn't pass on the charges.
Occupiers said they planned to stay in the building and would peacefully resist arrest and link arms if they were forced to leave.