President Mamnoon Hussain told students that it was a Western tradition and conflicted with Muslim culture.
His remarks came after a district in north-western Pakistan banned Valentine's Day celebrations.
Valentine's Day is popular in many cities in Pakistan, but religious groups have denounced it as decadent.
Earlier this week, the local government in Kohat, in Khyber Pakhtunkhwa, told police officers to stop shops from selling Valentine's Day cards and items.
Kohat district is run by a religious political party and borders Pakistan's conservative tribal areas.
Meanwhile, the Peshawar local council also passed a resolution to ban celebrations of what it called a "useless" day.
Kohat district administrator Maulana Niaz Muhammad told the BBC Urdu: "Valentine's Day has no legal grounds, and secondly it is against our religion, therefore it was banned."
While giving cards and flowers was not in itself a bad thing, linking this to a specific day was not appropriate, Mr Muhammad said. He added that he felt such practices could encourage obscene behaviour.
However, officials in both places later said the bans had been discarded or ignored for being unpopular.
Earlier this week, there were unconfirmed media reports that Valentine's Day gifts had been banned in the capital Islamabad - although this was subsequently denied by the government.
