According to the California Highway Patrol, which is responsible for security at the building, the threat was received in an email message.
A staffer for state Sen. Susan Rubio (D-Baldwin Park) confirmed that everyone inside the Capitol building was ordered to leave.
CHP officers conducted a search of the building on 10th Street in Sacramento, and Capitol employees were asked to work from home for the time being.
Just after 2 p.m., officials said the threat was determined to be unfounded.
In a statement, officer John Ortega said, "No suspicious items were located, and the buildings have been reopened at the direction of the Joint Rules Committee."