Two men attacked Omar Sayyed Sayyed, 24, on Saturday night in the Matariya district of the capital and stabbed him to death, family members said.
A security official said police had arrested both attackers who had confessed to killing Sayyed.
He said they had insisted they committed the murder because Sayyed was flirting with the sister of one of them.
But the relatives of the dead man denied this, saying the attack was politically motivated and that it occurred while Sayyed was putting up posters.
Sayyed's father, Sayyed Sayyed Mohammed, is an independent candidate in Sunday's parliamentary poll.