The university said on its Twitter page that the lockdown at Sweeney Hall was ended a little before 11 a.m. Thursday.
University spokeswoman Pat Lopes Harris says authorities received a report of a gunman around 9 a.m. She said there were no reports of injuries.
The San Jose Mercury News says a student reported seeing a man dressed in black clothing holding a gun in Sweeney Hall. Students and faculty inside the building had been ordered to shelter in place.
The rest of campus remained open while police swept the building.
Sweeney Hall houses the school's College of Education.
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