The man, identified as Yaqub, was convicted of stabbing another man to death on the street in October 2010, and sentenced to death by hanging in public, Fars said.
Yaqub was also sentenced to 100 lashes for an "immoral" relationship with the the victim's fiance and to 74 lashes for "demonstration of power" with a knife in public.
Mahmood Amiry-Moghaddam, the spokesperson for Iran Human Rights, called the punishment barbaric and urged the world community to condemn it.
Seven convicted drug traffickers were hanged in a prison in Iran's eastern Kermanshah province, its public prosecutor Mojtaba Maleki said on Monday, cited by state news agency Irna.
After China, Iran is the country which executes the highest number of people annually, according to Amnesty International. The Islamic Republic executed at least 388 people in 2009, according to Amnesty.