Although someone had been in the office less than an hour earlier, no one was in the building at the time of the incident.
No One was hurt and there were no witnesses.
Sheehan is running against Rep. Nancy Pelosi, D-Speaker of the House, for the 8th Congressional District seat.
"It seems to have been a calculated intimidation tactic," said Tiffany Burns, the Cindy for Congress campaign manager. "One of our computers was stolen, but no other property was taken from our offices and no surrounding buildings were targeted. Clearly they wanted to both frighten us and to gather information."
Total damage to the campaign office is currently estimated at more than $5,000.
Campaign officials said they have noticed a series of unusual events, including other threats of violence, in a statement issued on Oct. 13.
In that statement, Sheehan said, "the past few weeks have been a little strange at Cindy for Congress. The things that have been happening could just be coincidences, or a run of bad luck, but the climate for the possibility of campaign hanky-panky certainly exists."
Sheehan campaign staffers said that each incident followed closely on the heels of a confrontation between Sheehan's and Pelosi.
Thursday morning's incident occurred after an on-air confrontation between the two candidates on KQED's public affairs program Forum with Michael Krasny.
"Each time we confront her, each time we ask her for a debate, each time we gain ground in the polls, something horrible happens," said Burns. "Once or twice might be a coincidence, but such a consistent correlation is hard to ignore."