Most computers are not grounded, so if you are grounded while working on your computer, you are likely feeling the discharge of your ungrounded computer running through you to get grounded.  

Look at your computer charge cord -- if it is only two prongs, it's ungrounded and you are likely feeling the tingles and small shocks of your computer when you touch it.

To ground your computer not only spares you from feeling this sensation, but it will actually ground you as well (no need for a separate grounding tool) if your computer has a metal body that you are touching while you are using it.  

All you need to ground your computer is a USB port on your computer and this cord.  Plug it in and your computer is grounded (and so are you when you touch it!). Keep in mind this cord grounds your computer but does not connect to the electrical port of your outlet, so will not charge your computer, only ground it.

For more safety devices to use while on your computer, check out these items: