Nasser Bin Ghaith was convicted of promoting "false information in order to harm the reputation and stature of the state and one of its institutions" over a series of tweets in which he said he had been denied a fair trial in a previous case, the Beirut regional office of the rights group said.
Bin Ghaith's sentencing comes less than two weeks after the arrest of Ahmed Mansoor, another member of a group of rights activists known as the UAE Five, who were arrested in April 2011 and released later that year by a presidential pardon.
The five were accused of insulting UAE leaders online, inciting anti-government protests and calling for the boycott of elections for the Federal National Council, an advisory body with no legislative power.
Bin Ghaith was re-arrested in August 2015 over what Amnesty said was a series of tweets in which he said he was not given the right to a fair trial after his 2011 arrest.
Bin Ghaith's last tweets, dated August 2015, are widely critical of governments across the Arab world.
Ahmed Mansoor, who had been stripped of his passport and barred from travel despite the presidential pardon, was re-arrested this month under the UAE's cybercrime law.
He is accused of using social media platforms to "publish false information and rumours, and spread tendentious ideas that would sow sedition, sectarianism and hatred and harm national unity and social peace, as well as harming the state's reputation and inciting disobedience," according to the state-run Emirati news agency WAM.
Mansoor in 2015 won the Martin Ennals award, named after a former secretary general of the London-based Amnesty International.
The award, dubbed the Nobel Prize for human rights, is given to human rights defenders who show deep commitment to their cause despite huge personal risk.
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