Mehsud, who had headed the group locally known as the Tehreek-e-Taliban Pakistan, was killed in a drone strike last Friday. The TTP is different from the Afghan Taliban and is believed to be linked to al-Qaida.
CNN, quoting Azam Tariq, a member of the TTP's Shura Council or the group's main decision-making body, reported Shaheen was voted to become the interim head as it would be days before the group picks a permanent successor to Mehsud. There had been a $5 million reward on Mehsud announced by the United States.
Mehsud became TTP leader in 2009 after the death of fellow clan member Baitullah Mehsud, who also died in a suspected U.S. drone strike.
China's official Xinhua News Agency, citing local media, also reported Shaheen had been picked as the interim leader after differences emerged among TTP's various ranks in picking a successor.
Xinhua said earlier reports had said Khan Syed, also known as Khalid Sajna, would succeed Mehsud but quoted a TTP spokesman from the South Waziristan chapter as denying the report and that a new head would be announced in a few days.
Asmatullah Shaheen, who also goes by the name of Asmatullah Bhittani, leads the TTP's northwestern tribal region in South Waziristan, Xinhua said. Shaheen, who is on a list of 20 most-wanted Taliban militants in Pakistan, is also the head of a decision-making committee which will choose the new chief.
Mehsud, believed to be 34, was killed last week along with his aides in the drone strike that had targeted his vehicle and house in North Waziristan. His funeral was held Saturday at an undisclosed location, reports said.