50Hz noise affecting my oscilloscope and i want to know how to stop it
As you say your probe is an antenna. With an open high impedance end it can develop a few millivolts simply from mains pickup. Once you connect that end to your circuit that high impedance point goes away and most of the pickup.

If it does not you could consider getting a better quality lead but I dont really think that will be necessary unless the one you have is really bad.

As an additional practical suggestion route mains cables well away from your test rigs