Islamabad - The army also announced it would execute another man for carrying out an attack on soldiers in the city of Karachi.
The men were convicted by military courts established in the wake of the December 16 siege last year, while a seventh man was handed a life sentence for his role in the attack.
"The convicts were given fair trial by following all the legal formalities and offering/providing them legal aid and defence counsels. Today the sentences of death have been confirmed by the Chief of Army Staff," a statement issued on the military's website said.
The army also announced it would execute another man for carrying out an attack on soldiers in the city of Karachi.
The attack on the Army Public School in Peshawar led to widespread outrage, with officials announcing a slew of measures aimed at combating terror.
The government lifted a six-year moratorium on executions -- initially only for people convicted of terrorism but later extended to all capital offences.
Pakistan also amended its constitution to allow military courts to try terror suspects. Despite previously having specific anti-terror courts, cases dragged on for many years and many suspects escaped punishment due to legal loopholes or lack of witnesses, who would often not appear out of fear of repercussions from militant groups.
Pakistan's troops have been engaged in a full-scale offensive against Taleban and other militants in North Waziristan and Khyber tribal districts since June last year.
At the time of the Peshawar attack, the Taleban said it was retaliation for the army's continuing operation against militants in the tribal areas.