The statue base makes me think this is a famous cult image from some temple in
Stobi, without any connection to the
river gods beyond the locality.
One would expect that same statue to be depicted on other coins of
Stobi, but apparently this is not the case. Hopefully Whitetd49 can confirm this from the
Stobi monograph which I do not have.
A nude male god standing l. in a temple at
Stobi, extending r. hand and with
scepter in l., but not on a base and above all not placing r. foot on anything,
RPC II pl. 14, 311.
Apart from Neptune,
Mars can also place
his r. foot on something, a helmet,
cuirass etc., and probably a number of other deities too. So I would hesitate to
opt for Neptune, unless
his scepter/spear could clearly be identified as a trident on another specimen!