Hojat-ol-Islam Ahmad Khatami said in a statement on Tuesday that the gathering had been slated for August 17.
All the preparations had been made for the meeting and the secretariat was ready to hold it but it was postponed to a later date due to the continuation of the coronavirus pandemic, he said.
He added that the new date of the gathering will be announced once the situation improves.
The Assembly of Experts is a high-ranking body that elects and oversees the activities of the Leader of the Islamic Revolution.
Members of the assembly are directly elected to office by people for an eight-year term. It holds biannual meetings to appoint a new chairman.
Elsewhere in the statement, Hojat-ol-Islam Khatami underlined the need for observing the health protocols by those attending the mourning rituals in the lunar Hijri month of Muharram (starts on August 21), which mark the martyrdom anniversary of Imam Hussein (AS).
Shia Muslims around the world mourn the martyrdom of Imam Hussein (AS), the Sayyid-ul-Shuhada (master of martyrs), in Muharram.
The third Shia Imam (AS) and a small group of his followers and family members were martyred by the tyrant of his time - Yazid Bin Moaweya, in the battle of Karbala on the tenth day of Muharram (known as Ashura) in the year 680 AD.