At least 120 people were wounded in the blasts at the training centre for the Frontier Constabulary in Shabqadar, Charsadda district.
After early suspicions that one of the bombs was planted, police said both blasts were suicide attacks.
The Pakistani Taliban said they carried out the attack to avenge the death of Osama Bin Laden earlier this month.
The al-Qaeda leader was killed during a US commando raid in the northern Pakistani town of Abbottabad on 2 May.
Friday's attack came hours before army chiefs appeared before parliament to explain their actions over Bin Laden's death.
At the closed-door briefing, ISI chief Lieut-Gen Ahmed Shujaa Pasha is reported to have told MPs that he had offered his resignation after the Navy Seals raid, but had been turned down by the army chief.
The bombings happened as newly trained cadets from the Frontier Constabulary were getting into buses after completing their course.
The Frontier Constabulary is used to police the regions bordering Pakistan's tribal areas.
"Both attacks were suicide attacks," said the police chief of Charsadda district, Nisar Khan Marwat.
"The first suicide bomber came on a motorcycle and detonated his vest among the Frontier Constabulary men," AFP news agency quoted him as saying.
"When other [Frontier Constabulary] people came to the rescue to help their colleagues, the second bomber came on another motorcycle and blew himself up."
At least 66 of the dead were recruits, but there were also civilian casualties, officials say. A number of vehicles were destroyed in the blast.
"I was sitting in a van waiting for my colleagues. We were in plain clothes and we were happy we were going to see our families," Ahmad Ali, a wounded paramilitary policeman, told AFP.
"I heard someone shouting 'Allahu Akbar' [God is great] and then I heard a huge blast. I was hit by something in my back shoulder.
"In the meantime, I heard another blast and I jumped out of the van. I felt that I was injured and bleeding."
Lady Reading hospital in Peshawar has been inundated with casualties and doctors said they were fighting to save the lives of 40 critically injured cadets.
"It's the first revenge for the martyrdom of... Bin Laden. There will be more," Taliban spokesman Ehsanullah Ehsan told the Reuters news agency by telephone from an undisclosed location.
Shabqadar lies on the border with Afghanistan, about 35km (22 miles) north-west of Peshawar, not far from the militant stronghold of Mohmand.
The BBC's Aleem Maqbool in Islamabad says the security forces have often been the target of such attacks as they fight the Pakistani Taliban across the north-west of the country, but Friday's bombing is the deadliest attack this year.
He adds that the Pakistani army - which has come under intense scrutiny and criticism over the Bin Laden affair - is likely to point out that this attack is an illustration of the sacrifices it has made in the "war on terror".'Living dead'
After Friday's parliamentary briefing, Pakistan's information minister said Lieut-Gen Pasha had told MPs he was ready to take responsibility for any criminal failing.
"If any of our responsibility is determined and any gap identified, that our negligence was criminal negligence, and there was an intentional failure, then we are ready to face any consequences," said the minister, Firdous Ashiq Awan, citing the general.
Mr Awan told Express TV that killing Bin Laden had been a shared US-Pakistani goal but the Americans had breached Pakistan's sovereignty by going after him on their own.
The spy chief also told parliament Bin Laden had been isolated and "living like a dead man", the minister said.
"We had already killed all his allies and so we had killed him even before he was dead," Mr Awan cited Lieut-Gen Pasha as saying.
Our correspondent says many politicians and members of the public appear to be less concerned about Bin Laden's presence in Pakistan and more about the way the US was able to carry out its raid without official permission.
The US gives billions of dollars in military and humanitarian aid to Pakistan, but has questioned its reliability as an ally in combating the militants.
In recent years, Taliban militants have killed hundreds of people in bombings and other attacks across Pakistan.