The victim, whose name was not reported, was being held at a police station in Dadu after burnt pages of the Koran were found in a mosque, the BBC reported Saturday.
Hours after he arrived at the police station, a mob of people showed up, seized the man and killed him, authorities said. The victim's body was then set on fire.
District police chief Usman Ghani said the incident was recorded on cell phones and that police are reviewing video to try to identify the culprits.
Thirty people have so far been detained in connection with the attack, including the local police chief and five officers for failing to protect the man.