The Alexandria-based activist Hassan Mostafa was sentenced Saturday by an appeal court to one year in prison. Mostafa was appealing a two-year prison sentence he received earlier in March.
The 30-year-old marketing manager was found guilty of assaulting a justice ministry official.
He was arrested 21 January after attempting to file a complaint with Alexandria's prosecutor general on the absence of lawyers for dozens of detainees arrested in 20 January protests.
Mostafa was charged with physically attacking and verbally abusing prosecutor Ahmed Darwish while attempting to file his complaint.
Supporting activists claim the charges were fabricated. Several demonstrations have been held in the coastal city campaigning for Mostafa's release.
Dozens of activists who came out in solidarity protested the verdict at the appeal court Saturday.