At least 33 of the executions have been carried out within the past week, Amnesty International said in a statement issued Thursday.
The statement said 21 of the executions so far this year were officially reported by the Iranian government, while the other 19 were made known by reliable sources.
"The spike in the number of executions carried out so far this month in Iran is alarming. The Iranian authorities' attempts to change their international image are meaningless if at the same time executions continue to increase," said Hassiba Hadj Sahraoui, Amnesty International's Deputy Director for the Middle East and North Africa.
Most of those killed were convicted on drug-related charges, Amnesty International said.
"In Iran drug-related offenses are tried in Revolutionary Courts which routinely fall far short of international fair trial standards. The reality in Iran is that people are being ruthlessly sentenced to death after unfair trials, and this is unacceptable," Sahraoui said.
Iranian President Hassan Rouhani has said restrictions on civil liberties will be relaxed, Khaama Press reported, but the Iranian Human Rights Documentation Center said more than 300 people have been executed in Iran since Rouhani was inaugurated in August.