This paper addresses the frequency offset estimation problem in the presence of the timing error for OFDM-based WLAN systems. When the timing error exists, the correlation value used for the frequency offset estimation could be reduced significantly due to the timing error, resulting in considerable degradation in estimation performance. In this paper, using the coherence phase bandwidth (CPB) and a threshold, a novel frequency offset estimation algorithm is proposed and based on which, an efficient timing error estimation algorithm is also proposed for the re-estimation of the frequency offset.