Bahman Salimian, who was convicted for murder at age 15 and is now 27, may be executed as early as February 4, his lawyer told Radio Farda.
The execution had previously been scheduled for February 9.
Iran has the second-highest execution rate in the world, and is one of only a few countries that continues to execute juvenile offenders in spite of international demands for a halt to the practice.
Iran executed nine juvenile offenders last year, according to the European Union, which has repeatedly called on Tehran to abolish the death penalty.