The decision pronounced under Judge Hani Mustafa, confirmed a prior verdict by a criminal court that ruled Abdel-Fattah had protested illegally, endangered the public interest, and stole a police radio. Street protests have been effectively banned in Egypt.
Activists took to social media to decry the decision, the latest in an unprecedented crackdown on dissent under President Abdel-Fattah el-Sissi, a former general who led the military overthrow of his elected but divisive Islamist predecessor in 2013.
"I'm sorry. Our hearts are with everyone who's been following us and rooting for Alaa and justice," said Abdel- Fattah's aunt Ahdaf Soueif, a novelist and rights advocate, following the verdict.
An outspoken blogger, Abdel-Fattah has been in and out of prison in the years since the 2011 ouster of autocrat Hosni Mubarak.
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A software engineer by profession, he also campaigned for democracy and against the policies of the military council that ruled Egypt for nearly 17 months following Mubarak's ouster.
He has also opposed Islamist President Mohammed Morsi, and el-Sissi, who led Morsi's overthrow in 2013. Abdel-Fattah now has around a year-and-a-half remaining in his sentence, although he also faces another sentencing in December over accusations he insulted the judiciary.