They left the city of Ahvaz toward the Shalamcheh border crossing on Tuesday.
Arbaeen, which is one of the largest religious gatherings in the world, comes 40 days after Ashura, the martyrdom anniversary of the third Shia Imam, Imam Hussein (AS).
Each year, a huge crowd of Shias flock to Karbala, where the holy shrine of Imam Hussein (AS) is located, to perform mourning rites.
This year, Arbaeen falls on Thursday, November 9.