Many students have been arrested after the brutal attack in the northern city of Mardan, and the campus has been closed.
Reports suggest that two young men were accused of posting offensive content on Facebook. One survived with injuries.
Blasphemy is a highly sensitive and incendiary issue in Pakistan.
Critics say blasphemy laws, which allow the death penalty in some cases, are often misused to oppress minorities.
There have been other cases where people accused of it have been killed by an angry crowd.