What power supply and/or charger are you using?
Is it plugged into a 3 prong outlet? Does the outlet have a good ground (homes built before the 80 frequently have poor ground wiring to the outlets)?
Is your charger or power supply modified in any way (perhaps one of those McGuyver'd dual server power supplies)?
If all that checks out fine, then you just need to discharge yourself before touching it. Either touch something metal in the area first (iron railing, table/chair leg, door knob, screw on an outlet/switch cover, etc.) or invest in a static discharge mat/strap to use before touching the charging station.