For alleviating the high peak-to-average power ratio (PAPR) problem of orthogonal frequency division multiplexing (OFDM) while improving the bit error rate (BER) performance, the OFDM combined with time division multiplexing (TDM) using frequency-domain equalization (FDE) was recently proposed. In this paper, the theoretical BER analysis of the OFDM/TDM in a frequency-selective fading channel is presented. A conditional BER expression is derived, based on the Gaussian approximation of the residual inter-symbol interference (ISI) after FDE, for the given set of channel gains. Various FDE techniques, i.e., zero forcing (ZF), maximum ratio combining (MRC) and minimum mean square error (MMSE) criteria are considered. The average BER performance is evaluated by Monte-Carlo numerical computation method using the derived conditional BER expression.