Maikel Nabil, an Egyptian internet activist, has been sentenced by a military court to three years in jail for criticising the armed forces.
Since president Hosni Mubarak resigned on February 11, the military has been ruling the country.
The conduct of the military court has been criticised by Mr Nabil’s lawyers.
“We are in a state of shock because [on Sunday] they told us the decision would be on Tuesday, so the family and lawyer left. Afterwards the court announced its decision,” said Gamal Eid, a lawyer who heads the Arabic Network for Human Rights Information.
The 26-year-old blogger was found guilty of “insulting the military” and of publishing false news.
His lawyers said they would appeal the ruling.
Last week Human Rights Watch (HRW) had called for the charges to be dropped, saying Egypt’s armed forces “should drop all charges against (Nabil) for his Internet posts critical of the military”.
Mr Nabil, a campaigner against conscription, was arrested by military police on March 28 and his posts and comments on social networking website Facebook were used as evidence against him in the trial, his lawyers said.
“This trial sets a dangerous precedent at a time when Egypt is trying to transition away from the abuses of the Mubarak era,” Sarah Leah Whitson, HRW’s Middle East and North Africa director, said.
It is the first time a blogger is judged by a military court since the Supreme Council of the Armed Forces assumed control after president Mubarak resigned.
A military court sentenced another blogger to six months in prison last year for publishing “military secrets”. He had posted instructions on Facebook on how to enlist in the armed forces, his lawyers said at the time.
Another blogger who published a post on alleged patronage in a military academy was acquitted.
Dozens of people have been sentenced by military court in recent weeks for crimes including robbery and assault.
According to rights groups the trials are speedy and can result in harsh sentences.
The military promised to hand power to a civilian government after parliamentary and presidential elections.