JMMonteiro1990 :
I guess it is properly grounded as the other stuff connect to the same outlet is working fine and with out any type of static electricity. Im in Portugal btw
If the sensation goes away after the initial touch, chances are it is static electricity (ESD). If it remains after first touching the metal I/O shield, then it is electrical leakage. I'm not familiar with the electrical wiring codes in your part of the world, but there are inexpensive devices to test for incorrect outlet wiring. That would be the first thing I would do; eliminate the electrical system as the problem.
If you determine it is ESD, I would recommend simply touching some part of the case like you've been doing before doing anything inside the PC. Or even inserting a flash drive. One of my PCs is prone to ESD. Nothing I've found has remedied the problem. It seems to be a motherboard design fault.