This problem is probably caused by accidentally hitting the pointer device in the centre of the keyboard when typing.
To avoid this issue you need to disable the pointer device. This can normally be done through the Control Panel settings, but you haven't specified your operating system (e.g. Windows XP, Vista, Windows 7)
If you reply here and tell me what your operating system is I will be pleased to give you detailed instruction on how to discable the pointing device.
Answers & Comments
This problem is probably caused by accidentally hitting the pointer device in the centre of the keyboard when typing.
To avoid this issue you need to disable the pointer device. This can normally be done through the Control Panel settings, but you haven't specified your operating system (e.g. Windows XP, Vista, Windows 7)
If you reply here and tell me what your operating system is I will be pleased to give you detailed instruction on how to discable the pointing device.