"We plan to challenge the ruling against my client Hamad al-Naqi in the appeals court and we are very optimistic that the higher court will cancel the sentence," Shatti said.
Naqi, aged 22, was also charged with insulting the Gulf regimes of Saudi Arabia and Bahrain and for spreading false news that undermined Kuwait's image abroad.
The charges were based on a number of tweets on his Twitter account, but Naqi told the interrogators that his account had been hacked, the lawyer said.
Naqi was arrested about three months ago and has been behind bars ever since.
In recent months, Kuwaiti courts have issued jail terms against tweeters and activists amid a sharp rise in sectarian tensions between the emirate's Sunni majority and Shi'ite minority.
Parliament, which is controlled by Islamists and conservatives, last month passed a law stipulating the death penalty for serious religious offences, but the bill has not yet been enacted.