If so, then I doubt your motherboard will fry, as it would've fried the first time you touched it. I'd guess you just have a loose cable in the computer thats not being used, and is just touching the case.
It called electrostatic discharge or ESD for short. If you walk across a carpeted floor and touch a door knob you will sometimes get a small shock. If the grounding isn't that good on any electrical appliance even a pc you can get a "ZAP"! due to static buildup. It won't frie a keyboard but will give you a small sting at times. It sounds like the case needs a better common ground and surge protection.