Firmus (died 375) was a Berber Numidian prince and Roman usurper under Valentinian I. Firmus was the son of the Berber Jubaleni prince Nubel, a powerful Roman military officer, as well as a wealthy Christian. When Nubel died, Firmus killed his half-brother Zammac, who had illegitimately appropriated Nubel's wealth, and became successor to his father. His body was transported, allegedly on the back of a camel, on Theodosius' return to Sitifi, as proof of the end of the revolt.