Current flowing through neutral to ground
how does the current flow from neutral to ground through human body sometimes when both of them are at same potential


Current can only flow through your body if a high enough voltage is applied across it so if neutral and ground are actually at the same potential (they are often connected somewhere), and your finger is touching neutral and you are standing on the ground, this won't happen. That may not always be the case though...

Might help to do more research specifically related to grounding and ground faults.