1. A method for setting an initial frequency by a user equipment (UE) in a mobile communication system in which the UE performs an initial cell search in order to identify a Node B with which the UE can exchange data, the method comprising the steps of: performing a step# 1 cell search on predetermined frequency hypothesis hypotheses through a primary synchronization channel; storing the cell search result; determining an initial frequency offset estimation value from the cell search results for the predetermined frequency hypothesis; and estimating a frequency offset using the determined initial frequency offset estimation value.