The present article deals with the methodological treatment of the problems connected with the interpretation of a series of astral omina concerning the political life of the Pontus king Mithridates VI Eupator (about 120-63 B.C.), as referred to by Classical authors like Pompeus Trogus (via the Epitomae of Justinus, XXXVII, 2, 1-3) or Seneca (Naturales Quaestiones VII, 15, 2). If some scholars have tried to find the explanation of these events invoking some presumed Iranian religious patterns, this study shows that in reality these attempts are completely groundless, not only with direct reference to the properly Zoroastrian sources, but also to the more complex and pertinent astrological literature. The political use and abuse of these astral events for propaganda needs can be better framed without assuming a pseudo-Iranian favourable vision of the comets or of the falling stars. More reasonably, Mithridates VI, having lived between different cultures, knew well the Mazdean hostile tradition, which considered all these unpredictable celestial bodies as demons, not only and simply for a superstitious hostility, but according to a clearly framed theological interpretation of the world and of its cosmology.