In this paper, the effect of the carrier frequency offset (CFO) on system performance was investigated by computer simulations in single carrier Frequency Division Multiple Access (SC-FDMA) system. By computer simulations, figures of signal-to-noise ratio (SNR) versus symbol error rate (SER) of the system with and without CFO are obtained. Besides, the figure of SNR versus SER is obtained for different CFO values. From these results, it is seen that when the value of CFO increases, the performance of the system decreases. Moreover, the figures of SNR versus SER is obtained for different FFT sizes and different modulation levels for the same CFO value. It is seen that when the size of FFT increases, the system yields better performance. When the level of modulation increases, the performance of the system decreases. In addition, the estimation of CFO is performed by computer simulations. In the simulations, the estimation algorithm based on cyclic prefix is used. The figures of mean square error (MSE) versus SNR related with estimation and different modulation levels are obtained. It is seen that MSE decreases when SNR increases. By using CFO values obtained with estimations, correction process is also performed to obtain performance values of the system.