The convicts' death sentence was upheld by a military court in March, following a trial in which the six were convicted of carrying out attacks after the ouster of Islamist president Mohamed Morsi in July 2013.
The defendants were charged of planning terrorist operations, attacking military personnel, army facilities, naval ships, and being members of the Sinai-based militant group Ansar Beit Al-Maqdis.
Death sentence was handed down to seven Islamists, including one in absentia, in the last year's case known as 'Arab Sharkas'.
'Arab Sharkas' is a village in the Qaliubiya governorate, north of Cairo, where security forces carried out a raid in March last year against a terrorist cell in which two military officers were killed.
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Rights groups had sent letters to the National Council for Human Rights and the Presidency last month, requesting them to stop the executions.
Amnesty International said the men underwent a "grossly unfair" trial and that the only witness during the trial was a secret police officer.