|Previous attacks on minorities over blasphemy allegations have led to protests|
Their bodies were burned at the brick kiln where they worked in the town of Kot Radha Kishan in Punjab province.
Police identified the victims only as Shama and Shehzad, AFP reports.
Blasphemy is a highly sensitive issue and critics argue the laws are often misused to settle personal scores and that minorities are unfairly targeted.
"Yesterday an incident of desecration of the holy Koran took place in the area and today the mob first beat the couple and later set their bodies on fire at a brick kiln," local police station official Bin Yameen told the AFP news agency.
A security official told the BBC that local police had tried to save the couple, but they were outnumbered and attacked by the angry crowd.
Senior police officials and government ministers have now arrived there to investigate the killings.
In May gunmen in the city of Multan shot dead a lawyer, Rashid Rehma, who had been defending a university lecturer accused of blasphemy. This is how absurdly insane many Pakistanis are about the Quran and the prophet. Apparently, Allah is so weak that he has to be protected by out-of-control people. The God of Christians and Jews is very capable of defending Himself. When one blasphemes against our God we usually only have pity for him knowing that he has a long, painful future awaiting him.
It's curious why Muslims are so fanatic about Mohammed when the Quran tells us about Isa, who was born of a virgin, performed many miracles, and will sit on the Judgement Seat on that great and terrible day. They persecute the children of the Son of God in the name of a mere prophet. How do you think that will serve them when they stand before that very Son of God?
And last month a Pakistani court upheld the death penalty for Asia Bibi, a Christian woman convicted of blasphemy in 2010 - a case which sparked a global outcry.
Since the 1990s, scores of Christians have been found guilty of desecrating the Koran or of blasphemy.
While most of them have been sentenced to death by the lower courts, many sentences have been overturned due to lack of evidence.
However, correspondents say even the mere accusation of blasphemy is enough to make someone a target for hardliners.
Muslims constitute a majority of those prosecuted, followed by minority Ahmadis.