Musharraf has spent the last five years in exile in London and Dubai after resigning in 2008, CNN reported.
In a video message posted online, Ehsanullah Ehsan said a "death squad" from Tehrik-i-Taliban would be sent to kill him.
Musharraf has announced he will fly into Karachi Sunday and attend a rally intended to signal his plan to lead his party in the country's general election in May.
Adnan Rasheed, who was convicted of engineering an attack on Musharraf in December 2003, will lead the suicide bombers, Ehsan told Dawn News.
Rasheed was sentenced to die for the attack, but escaped from prison in April 2012 along with other inmates.
Musharraf joined the U.S. war on terror after the Sept. 11, 2001, attacks, angering the Taliban, and later instituted a major crackdown on militants in Pakistan.