ODM National Elections Board Chairperson Judith Pareno said the party will announce new dates soon.
The elections were to be held at the Bomas of Kenya.
Pareno said the move is aimed to allow time to resolve disputes that had arose last weekend during elections in the city.
The exercise was postponed from last weekend to September 13 and 14, following complaints lodged by various stakeholders.
The National Election Board said 37 disputes were filed by contestants, which necessitated the pushing forward of the county polls.
The party has conducted and concluded grassroots elections in six counties in the last three weeks.
They include Marsabit, Wajir, Kajiado, Vihiga, Migori and Kilifi.