Wang Chao-hung, better known as "Teacher Wang", was ordered to pay almost £900 ($1380).
He sparked panic and urged people to leave their homes for makeshift shelters made from converted cargo containers.
However the date – May 11 – came and went with no sign of the predicted apocalypse.
Prosecutors are investigating claims that he might have cooperated with container businesses to set up a shelter village in Nantou.
But yesterday a court in Nantou officially convicted him of 'spreading socially disruptive rumours' and slapped him with a fine.
Wang claimed that his remarks had been misinterpreted by journalists.