"We received an email from the FIVB announcing a change of plan," he said, adding that no reason was given for the decision.
"We are waiting to find out the real reason (behind the change) and we will then decide what to do," he added.
Argentina has been asked to take over from Iran and organise the 2015 under-19 games.
The FIVB spokesman said the reason to sanction Iran was taken after the federation held a meeting in October with a delegation from Human Rights Watch.
The rights watchdog asked the FIVB to take action against Iran following the arrest of Ghavami, who was detained June 20 after she tried to attend a World League volleyball match between Iran and Italy.
At the time the female fans were barred from attending the match at Tehran's Azadi (Freedom) Stadium.
The decision was contested by the government of President Hassan Rouhani, who advocates more social freedoms, while conservatives want to strengthen measures to prevent men and women from mixing.
National police chief General Esmail Ahmadi Moghaddam said in June "we cannot allow the presence of women in stadia" because gender mixing "is not yet in the public interest".
Women are also banned from attending football matches in Iran, with officials saying this is to protect them from the lewd behaviour of male fans.
No reason was given for the jailing on November 2 of Ghavami, but following her arrest in June she was accused of spreading propaganda, a broad charge used by Iran's judiciary.
Ghavami, a 25-year-old law graduate from London, has been on hunger strike since the verdict was pronounced against her, according to her brother.
FIVB president Ary Graca in a statement posted on the international federation's website says "women throughout the world should be allowed to watch and participate in volleyball on an equal basis."
Iran's volleyball team is one of the best and very popular at home.
It finished 6th in this year's World Championships in Poland and 4th at the World League.