Prosecutors said that three men and one woman were accused of founding a far-right group and procuring explosives.
They added that a previously unknown group, the “Old Schools Society”, had been planning to attack mosques and hostels for asylum seekers.
The suspects were arrested in raids across five German states involving some 250 investigators.
“In the search, pyrotechnics with large explosive power and further pieces of evidence were confiscated,” said the prosecutor’s office in a statement.