In composites consisting of a thermoplastic butadiene-styrene (SBS) elastomer matrix reinforced with oxidized short carbon fiber, scanning electron microscopy (SEM) reveals the existence of matrix-fiber interactions, which are not detected when employing commercial carbon fiber. Interpretation of the dynamic properties and other parameters, such as equivalent interfacial thickness, and glass transition temperature, measured in terms of maximum damping temperature, as well as the apparent activation energy of the relaxation process, helps to explain the existence of such interactions.