The blasphemy law has been widely criticised by human rights groups following the case of Asia Bibi, a Christian woman sentenced to death last month for insulting Islam.
Naushad Valiyani, a Muslim doctor in the southern city of Hyderabad, was arrested on Friday after a complaint to police alleging his actions had insulted the Prophet Muhammad, said regional police chief Mushtaq Shah. Police are investigating whether Mr Valiyani should be charged with blasphemy.
Muhammad Faizan, a drugs company representative, visited Mr Valiyani's clinic and handed out his business card. When the doctor threw the card away, Mr Faizan went to police and filed a complaint.
Dozens of Pakistanis are sentenced to death each year under the blasphemy law, though most cases are thrown out by higher courts and no executions have been carried out. The law, however, is unlikely to be repealed because the government's ruling party - largely secular - relies on the support of Islamist groups.
Islamist political parties have recently demonstrated in support of the law and the sentence against Bibi.