The Iranian was on trial along with 25 Kuwaiti Shias, one of whom was sentenced to life in prison. Nineteen were jailed for between five and 15 years, three were acquitted and one was fined.
The defendants were also convicted of spying for Iran-backed Lebanese Shia militia Hezbollah.
Kuwaiti authorities said in August they had dismantled an Iran-linked cell and seized large quantities of arms, explosives and ammunition.
The verdicts come amid deep tensions between Tehran and Gulf states after Iranian protesters on January 2 torched Saudi Arabian diplomatic missions in the Shia-dominated Islamic republic.
The attacks were in anger over Riyadh's execution of Nimr al-Nimr, a prominent cleric from the kingdom's Shia minority.
Riyadh cut diplomatic ties with Tehran the next day and a number of its Sunni Arab allies followed suit, including Bahrain and Sudan. Other Arab countries downgraded ties or recalled their envoys from Tehran.
Kuwait recalled its ambassador from Iran to protest the attacks and summoned Tehran's ambassador to express its disapproval.
