A seventh suspect remains at large.
Two of the men are also suspected of attacking two American Mormon missionaries in the capital, Pristina, two days before their November 5 arrest, a senior police official involved with the investigation said.
Authorities have grown increasingly worried about the rise of extremism in a country with a strong presence of NATO peacekeepers, including hundreds of US troops.
Authorities had followed the cell for three months after intercepting a call allegedly plotting an attack with another person of Kosovo descent in an unnamed European country, said the police official, who is part of a team that deals with terrorist threats.
Also Read
A sniper rifle, handguns and material for making an improvised explosive device were found in suspects' houses, according to the police official.
A justice official said the suspects had been watched by video surveillance, phone tapping, and email monitoring, but gave no further details because of the ongoing investigation. Both officials spoke on condition of anonymity because they were not authorised to discuss the matter.
Around 150 ethnic Albanians are believed to have joined foreign fighters battling the forces of Syria's President Bashar Assad and some 12 are believed to have been killed there.