Hi Zagi. I had the same thing a few months after starting on Imuran - around my upper chest and neck. My IBD nurse noticed them too and said to keep an eye on them and report if they kept getting bigger or darkened.
After a sort of initial crop of them broke out, I stopped getting new ones and they didnt seem to be be growing. I've been off it 6 months now but the moles are still there.
Try to stay out of the sun or wear sunscreen cos you burn easier on Imuran and some other medd like Mesalazine.