Kari Mokko, a spokesman for Prime Minister Jyrki Katainen, said the man was stopped before he was able to reach the prime minister.
The attempted attack occurred in the southwestern city of Turku, where Katainen was campaigning ahead of Sunday's municipal elections.
Mokko could not give any details on the suspect. He said the prime minister was not hurt.
(Copyright 2012 by The Associated Press. All Rights Reserved.)