Police seized explosives, detonators and several model airplanes while searching the flats of four suspects and a neo-Nazi venue outside Freiburg last week, they said in a statement.
The suspected ringleader of the plot, an unnamed 23-year-old man, was arrested. Last month he was caught throwing a firecracker at a demonstration by anti-fascist groups against a far-right protest in the western city of Dortmund.
Police said they also found chemicals, narcotics and a video camera at the sites.
While the number of far-right supporters in Germany is declining, the discovery in 2011 of a neo-Nazi cell blamed for the murder of nine immigrants has highlighted a violent underground fringe not previously acknowledged by authorities.
Germany's domestic intelligence agency estimates there are around 22,000 supporters of far-right or neo-Nazi ideology in Germany, a country of 82 million. Of these, around 9,600 are considered willing to use violence.