Police said Everett Basham, 45, is being held in the Santa Clara County Jail on suspicion of threatening Sen. Leland Yee of San Francisco.
According to officers, Basham was also booked for possessing a concealed firearm and they confiscated explosive materials at his home.
Yee's spokesperson, Adam Keigwin, said the Democratic senator received the threat and passed it on to the California Highway Patrol. Yee is not commenting on the case due to the ongoing investigation.
Keigwin told the Associated Press that the threat was made in response to the senator's legislative efforts to end gun violence.
Yee's SB47 would prohibit the use of so-called bullet buttons and other devices that allow for swift reloading of military-style assault weapons.
The Associated Press contributed to this report.