The group velocity of evanescent waves tin undersized waveguides, for insta
nce) was theoretically predicted, and has been experimentally verified, to
be superluminal (nu (g)>c). By contrast, it is known that the precursor spe
ed in vacuum cannot be larger than c. In this paper, by computer simulation
s based on Maxwell equations only, we show the existence of both phenomena.
In other words, we verify the actual possibility of superluminal group vel
ocities, without violating the so-called (naive) Einstein causality.