In this paper, we consider a single carrier frequency division multiple access (SC-FDMA) system impaired by frequency instabilities and timing offset. In this system, both time and frequency offsets deteriorate the orthogonality of subcarriers and generate multi-user interference which degrades the system performance. For fast and efficient design of such systems, it is crucial to have an analytical and accurate evaluation of the system performance. However, such closed-form expression for the error rate is available only for perfectly synchronized SC-FDMA systems in the literature. In fact, the performance of SC-FDMA systems in the presence of time or frequency offsets has only been evaluated based on simulations. In this paper, we analytically obtain the symbol error rate (SER) of an SC-FDMA system impaired by time or frequency offsets when data is transmitted over a frequency selective Rayleigh fading channel. Through comparative simulations, we show that our proposed analysis can accurately evaluate the SER performance of SC-FDMA systems in the presence of time and frequency uncertainties.