Kevin Joseph O'Connell was sentenced Wednesday but could soon be free because he already has served most of that time.
His public defender tells the Marin Independent Journal she expects him to be released next week.
O'Connell pleaded guilty to threatening a public official after a judge offered to reduce the charges to misdemeanors.
Authorities say O'Connell made a death threat against Boxer in a voicemail left at her San Francisco office in July. The threat apparently was not related to Boxer's political positions.
The 47-year-old O'Connell has also been ordered to serve three years of probation and avoid any contact with Boxer, her family and her office.