The executions took place Tuesday, a senior justice ministry official said.
"Twenty-one Iraqis were executed today, according to Article Four of the Anti-Terrorism Law," the official said.
The United Nations and Britain showed concern for Iraq's use of capital punishment and there were widespread calls from across the globe for a moratorium on the practice, Middle East Online reported.
The United Nations issued a report earlier this month saying while the use of the death penalty worldwide decreased last year, Iraq remained a black spot with 129 executions in 2012, the news agency said.
Justice Minister Hassan al-Shammari said last month Iraq would continue to implement capital punishment.