In this paper, we propose an iterative belief propagation (BP) detector over multiple-input multiple-output (MIMO) frequency selective fading channels as an alternative to the typically used maximum a-posteriori (MAP) or Viterbi detectors. Unlike the trellis based detectors having serial structure, the proposed detector has the advantage of having a parallel structure, resulting in more efficient and fast hardware implementations. Moreover, BP detector is less complicated than the MAP detector and it has a short decoding delay which is essential for reduced memory requirements. Via simulations we show that, over frequency selective fading channels, the proposed BP detector achieves a near-optimal performance, even in the presence of the length 4 cycles in the channel factor graph.