San Bernardino County sheriff's deputies detained two men during a traffic stop Saturday morning near the intersection of Twentynine Palms Highway and Old Woman Springs Road.
Officials say the deputies found live ammunition, gun powder and a military-grade explosive device inside the car.
According to the Southern Poverty Law Center, "sovereign citizens" are part of an extremist movement whose members consider themselves exempt from U.S. law and who sometimes use violent tactics. Many also maintain racist beliefs.
A search warrant was served at a sovereign citizen compound nearby.
Authorities said they found military-grade explosives, ammunition and firearms at the home.
Both men, identified as David and Jeffrey Russell, were prohibited from owning firearms, records showed.
A woman identified as Venus Mooney was also arrested at the compound, authorities said.
All of the explosives were disposed of safely.