The attacks late yesterday came hours after the country's Constitutional Court held the February 2 general elections invalid which has upset the ruling Pheu Thai party supporters.
The targets were a seafood restaurant, a petrol station and a brewery.
Four people were hurt but were out of danger, Chiang Mai police said.
The police think the motive could be political or personal. No arrests have been made so far.
Thailand has been in a political crisis since mass rallies began in November with protesters demanding an un-elected People's Council to replace Premier Yingluck Shinawatra's government.
The protesters accuse Yingluck of acting as a proxy for her fugitive brother, former premier Thaksin Shinawatra, who was ousted in a coup in 2006. He lives in self-exile in Dubai to escape a jail term on a corruption conviction.