Two other men were questioned and released. All three are suspected of resisting police.
The incident in took place in central Oulu on Saturday when the three men, who were passing out National Resistance leaflets, confronted a National Coalition party organization secretary who was taking photographs of his own party's candidates.
Police say the three provoked an incident over the photography and attacked the organization secretary and two other people. The three resisted police officers on the scene, who then used pepper spray and stun guns to subdue them.
All three, who are in their 20's, were detained for questioning. One, who is now in custody, was found to be wearing a bullet-proof vest.
According to police, the three have neither admitted nor denied the violations they are suspected of.