A spokesman of the Association of Muslim Scholars said Shaikh Dhamir al-Dhari was walking down a street near his mosque when gunmen opened fire from a car, killing him.
Al-Dhari was not a prominent member of the association, but his half brother serves as the organisation's secretary-general.
The body seeks to represent interests of the Sunni community and last week had in a statement said that "no one in his right might" would reject elections in principle "but at the same time we dont want to have nominal or hasty elections and pay a hefty price for that."
Al-Sifaidhy, the association spokesman said he expected more such attacks.
"We expect ... that Iraq would witness many of such operations to create chaos and strife," he said.
Lawlessness and anarchy have been sweeping Iraq since US-led forces took control at the end of the war.
Resistance fighters continue to mount incessant attacks that the occupation forces have till date failed to quell.
Ever since major combat was declared over by President George Bush on 1 May, 263 US soldiers have been killed in Iraq.
A total of 378 soldiers have died in combat since US forces first entered Iraq last March.