This paper proposes an adaptive decision feedback channel estimation (DFCE) scheme using the knowledge of terminal speed in single-carrier frequency-domain equalization (SC-FDE). Since SC signals generally have the large envelope variation in frequency spectrum, the subcarrier signals with the small magnitude cause the noise enhancement. The proposed scheme adopts DFCE only for the subcarriers with the relatively large magnitude. Moreover, the proposed scheme adaptively controls the forgetting factor according to the channel condition such as noise dominant channel and time selectivity dominant channel. The feature of the proposed approach is to theoretically derive the effect of time selective fading by using the terminal speed and to detect the actual channel condition. The effectiveness of the proposed scheme is demonstrated in comparison with the traditional DFCE with the fixed forgetting factor by means of computer simulations.