In this paper a new method for nondestructive testing (NDT), applied to carbon fiber composite materials, is investigated. The approach is based on the comparison between the electromagnetic signal reflected by the carbon fiber composite sheet under test, when an ultra-wideband (UWB) signal is incident on it, and the one reflected by a healthy sheet. The possible presence of a defect is then revealed by an appropriate metric measuring the mismatch between the two reflected waveforms. The performance of different metrics is investigated, for two defect types, based on real measurements in an indoor environment. As an outcome of our experimental activity, very promising results have been obtained for one of the tested metrics, which allows to accurately detect surface defects with a size comparable to the radar resolution on a carbon fiber composite sheet.