Investigators say the suspects gathered pyrotechnic materials, underwent firearms training and took other steps to prepare the planned attacks.
Daniel Brodowski, spokesman for the District Prosecutor's Office in Olsztyn, said the indictment had been filed with the district court.
The men were charged in stages over several months, with the first two detained in April, a third in early June and the fourth in September.
Brodowski said all four suspects are Polish citizens from Olsztyn and the surrounding area.
The investigation began after Poland's Internal Security Agency (ABW) uncovered the alleged plot while monitoring online forums, he said.
During searches, investigators seized electronic devices that they say contained evidence of preparations for terrorist acts, including instructions for making improvised explosive devices and Molotov cocktails.
According to prosecutors, the suspects expressed interest in targeting religious sites, schools and places frequented by ethnic and cultural minorities.
The men face charges including preparing terrorist acts by participating in firearms and military training, promoting Nazi and fascist ideology, publicly inciting terrorist murder, and illegally possessing pyrotechnic materials.
Prosecutors say the suspects also took concrete steps to facilitate the planned attacks by acquiring pyrotechnic and flammable materials and gathering information on potential targets and methods of constructing explosive devices.
(pu/gs)
Source: IAR/PAP, radioolsztyn.pl