The 53-year-old suspect, previously sentenced for unspecified other offenses motivated by far-right ideology, was arrested during a search of his apartment in Berlin, the prosecutor general in the western city of Frankfurt said.
He is accused of sending threats and hate messages over a three-year period to leftist national and regional politicians as well as to a Turkish-German lawyer who represented victims of far-right crimes.
The suspect signed his letters with the acronym "NSU 2.0," prosecutors said, a reference to the National Socialist Underground (NSU) group blamed for the killings of eight Turks, a Greek and a German policewoman between 2000 and 2007.
The main surviving member of the gang was sentence to life imprisonment in 2018.Interior Minister Horst Seehofer will on Tuesday hold a news conference about politically motivated crime in Germany, where authorities have stepped up efforts to combat far-right extremism since a pro-immigration politician was shot and killed and a synagogue was attacked by a gunman in 2019.