I was wondering if you could advise if this is an error struck coin…

Hard to say. First off, even if it is, it's not very dramatic and would not be likely to add much value. It's important to know whether that circular line is depressed (goes into the coin like a valley) or raised (sticks above the surface, like a ridge). It appears to be the latter, suggesting something pressed into the coin. That could easily be an event that took place after the minting process, which would be regarded as damage or alteration, not an error. So the unsatisfying answer is: it's hard to say, it's probably not, and even if it is, it's more interesting than important.