The attack came the same day the government announced the arrest of a senior al Qaeda operative on the FBI's most wanted list.
It was not clear who was behind the attack, but suspicion fell immediately on Islamic militants, angry over the government's decision to back the U.S.-led war on terrorism.
In December, there were two failed attempts to, who blamed al Qaeda for the bombings. On Thursday, the government acknowledged that it has held talks with Saudi officials about sending troops to Iraq as part of a Muslim peacekeeping force.
The bombing occurred at about 7:20 p.m. as Aziz, the finance minister who has already been tapped to take over as prime minister, was traveling through a bazaar in Fateh Jang, a town 35 miles southwest of the capital, Islamabad, said Mohammed Haidar, a local police official.
An Interior Ministry spokesman said at least four people were killed and 24 injured in the attack.
Haidar said Aziz's driver was among the dead but the senior politician escaped without serious injury. Geo Television reported six dead and 25 injured.
"I spoke with Shaukat Aziz. There was an explosion close to his car. His driver and a suicide attacker was killed," Sen. Mushaid Hussain, a member of Aziz's ruling Pakistan Muslim League-Q party told The Associated Press. "He was calm, cool and composed."
Aziz, a former Citibank executive credited with turning around Pakistan's economy under Musharraf, was in Fateh Jang to campaign for an upcoming bi-election in an effort to win a seat in the lower house.
Musharraf's ruling party has said they want him to be prime minister, but the senator must first gain a seat in the Aug. 18 vote to be eligible. A victory is all but assured.
Opposition parties have denounced the proceedings as an affront to Pakistani democracy, five years after Musharraf seized power in a bloodless coup.
After Prime Minister Zafarullah Khan Jamali stepped down last month, Chaudry Shujaat Hussain was appointed caretaker prime minister while the political maneuvering was completed to allow Aziz to step in.
The attack followed the announcement early Friday that Pakistan had arrested Ahmed Khalfan Ghailani, a Tanzanian on the FBIs most wanted list who is wanted for the 1998 twin embassy bombings in East Africa.
Hussain said there was no evidence that the two were linked.
The attack also follows two attempts by Islamic militants in December 2003 to assassinate Musharraf, the ultimate powerbroker in this conservative Islamic nation of 150 million people. The second attack was close enough to kill several members of his entourage and more than a dozen passers-by.