The group called on Finnish Members of Parliament and of the European Parliament to do all they can on behalf of the imprisoned candidates.
Police say that about 70 people participated in the public meeting. The main organiser of the event, Eva Neklyaeva, believes the number to be over 100 people.
Neklyaeva says that participants included representatives of the International PEN association of writers, Amnesty International, cultural personalities, Green League MPs and Belarusians living in Finland.
Neklyaeva is the daughter of one of the imprisoned presidential candidates, Vladimir Neklyaev. In Helsinki, she has directed the international Baltic Circle theatre festival.
After an election in Belarus about a week ago, election officials announced that Aleksandr Lukashenko had been re-elected for a fourth term with nearly 80 percent of the vote. A violent demonstration followed with allegations of vote-rigging, during which several opposition candidates were arrested. They now face 15 years of imprisonment.