Hmm, I don't know but that's a good question. Aurochs were extant until the 17th century and were native to the Roman empire region and beyond, so it certainly seems possible that they might appear on some ancient coins. It seems likely that many of the bulls shown on ancient coins could be aurochs. Limitations of die engraving (and engraver skill) might make definitive determination difficult since animal size is a main difference. Pliny supposedly mentioned aurochs but I haven't searched out those passages. You could try searching his Natural History to see if he mentions them in any geographic context, and then closely examine Roman provincial coins from those regions to see if any of the bulls/cattle on those coins could be aurochs. Aurochs weren't extinct until the 17th century so it certainly seems possible that they might appear on some ancient coins. Zebu, a domesticated Indian version of aurochs, appear on many ancient coins.
Thanks for that link, George. Got one from Seleukos I Nikator , a Macedonian General in Alexander the great's army,he inherited a large part of Alexanders empire, depicted is an ancient bull probably from Greece or from Syria.