Ultra-wideband (UWB) has been considered a viable and an innovative solution for future short-range high-speed wireless communication systems. One of the big concerns for UWB devices to function properly is the narrow band interference (NBI) issue, which must be carefully studied. For this purpose, the performance of UWB communication system over indoor Lognormal fading channel in the presence of NBI is evaluated. We model the NBI signal as a single tone interferer, and a closed form expression for the bit error probability (BEP) over frequency selective multi-path fading channel has been derived. In order to validate our analysis, a comparison with a previously evaluated performance of UWB system in Nakagami-m fading channels has been done. It will be shown that the narrow band signals have a noticeable impact on the performance of UWB systems in lognormal frequency selective fading channels.