Former lawmaker el-Erian, 52, and fellow Brotherhood leader Helmi al-Gazar were detained on 6 May hours before the staging of nationwide anti-government protests, which police alleged they had organised.
Few details were available on the other two ordered freed, who were among hundreds of rank-and-file Muslim Brotherhood members arrested, but later released, in a crackdown against political activists opposing the government of President Hosni Mubarak.
Later on Saturday, Brotherhood lawyer Abdel Moneim Abdel Maqsoud said el-Erian refused to pay bail of 2000 Egyptian pounds ($347), arguing that it was not required because he had not been charged.
Prosecutor Hisham Badawoui rejected the argument and said el-Erian would not be released without bail. Abdel Maqsoud said his client then agreed to pay and was expected to be freed on Sunday.
The Brotherhood recently held
protests demanding reform
Before he was most-recently jailed, el-Erian had spent five years in jail since 1995 on charges of belonging to a banned group that sought to create an Islamic state in Egypt.
The Egyptian authorities can hold detainees for up to six months without trial under much criticised emergency laws issued in 1981 after Islamic hardliners assassinated president Anwar Sadat.
The Brotherhood was established in 1928 and though banned in 1954 it is now tolerated. It has long refrained from provoking the government but has engaged in protests since March, demanding political reform.
The organisation, believed to be Egypt's largest Islamist group, is highly organised and remains a key player in Egyptian politics despite the ban and vilification in the state-run media.
It renounced violence in the 1970s and now has supporters sitting as independents in parliament, holding 15 seats as the largest opposition bloc.
The group has announced that it is planning to field 150 candidates in upcoming legislative elections scheduled for 9 November, but el-Erian is not expected to run.