Ein Khaing Oo, a reporter for the weekly Myanmar-language magazine Eco Vision, was arrested on June 10 while covering a demonstration by victims of the cyclone.
About 20 protesters were complaining about what they said was a lack of government assistance after the cyclone in May, which left about 150,000 people dead and millions homeless.
"This unjust sentence comes amid a wave of unprecedented sentences for journalists and activists," Reporters Without Borders, a media advocacy organisation, and the Burma Media Association said in a statement.
"We appeal to Burma's military authorities to free Ein Khaing Oo, whose only crime was to cover the humanitarian disaster in the Irrawaddy delta."
Reporters Without Borders said another journalist, Zaw Thet Htwe, and a blogger, Zarganar, were also being held for helping victims of Nargis.
Another 17 pro-democracy activists were jailed for between two and 16 years at hearings in yangon and Mandalay on Friday, according to legal sources.
Many of those jailed were involved in last year's mass protests against rising fuel and food prices, which developed into a display of opposition to military rule.
Nyan Win, a spokesman for the opposition National League for Democracy (NLD) party led by detained Nobel peace laureateAung San Suu Kyi, said that at least one dozen of those convicted on Friday were members of the group.
"Many more activists are expected to be sentenced to various prison terms in the next few days as the courts have been instructed to expedite all pending cases," a court official, who asked not to be named, told the Reuters news agency.
Up to 60 opposition activists are believed to have been jailed in the last two weeks.
New York-based Human Rights Watch said on Wednesday that recent weeks "show a more concentrated crackdown on dissent clearly aimed at intimidating the population" ahead of elections to be held in 2010.
Critics say the polls, which will be held under a new constitution confirmed by a referendum held just days after the cyclone hit, will merely be a way of entrenching the military's power.