The convicts were found guilty of various acts of terrorism in the country, including breaking of Bannu Jail, attacks on armed forces, law enforcement agencies and civilians, the army said in statement.
"Today Chief of Army Staff confirmed death sentences awarded to another 12 hardcore terrorists, who were involved in committing heinous offences relating to terrorism," it said.
The militants were tried by military courts set up after attack at Peshawar school on December 16, 2014 which killed at least 150 people, mostly students.
Already several militants convicted by these courts have been hanged, including the facilitators of the Peshawar school attack.