Television news footage showed numerous people in plastic cuffs being led away from the site by police around 5 a.m. The protesters did not appear to be resisting.
A message for a police spokeswoman was not immediately returned.
City officials had originally been supportive of the protesters, with Oakland Mayor Jean Quan saying that sometimes "democracy is messy."
But the city later warned the protesters that they were breaking the law and could not stay in the encampment overnight.
They cited concerns about rats, fire hazards, public urination and acts of violence at the site, which had grown to more than 150 tents and included health, child-care and kitchen areas.
But protesters over the weekend said they had no plans to leave.