Vikernes and his wife Marie Cachet were arrested on Tuesday at their home in a village in the central Correze region of France.
The interior ministry said Vikernes, a black metal musician and convicted killer, was "close to the neo-Nazi movement" and could have been preparing a "major terrorist act".
Vikernes, who also goes by the name "Varg", Norwegian for "wolf", had been under surveillance for several years.
But anti-terrorism authorities in Paris opened a probe into the father-of-three at the beginning of the month after his wife purchased weapons – albeit legally as she has a permit.
Officers seized five long-range weapons at their home including four 22 caliber Long Rifles.
Vikernes is notorious for having stabbed to death a guitarist from another black metal band. He spent 16 years in prison for the crime.
Interior Minister Manuel Valls conceded that they had as yet identified "no target, no plan", but intelligence chiefs had decided it was important "to act before and not afterwards".
"The DCRI (French domestic intelligence service) considered that messages he had posted on the Internet expressed great violence."
Vikernes' former lawyer in his murder trial on Wednesday criticised France for the arrest, calling the charges against him "thin."