This is often caused by the palm lightly making contact with the touchpad. It can usually be prevented by disabling tapping for the touchpad.

To test if this is the cause, try disabling the touchpad while typing. On many models, this can be done using a small button above the touchpad and below the keyboard or by using the FN+F9 key combination. If that solves the problem, re-enable the touchpad, and then disable tapping.

The setting is in the Mouse properties. In Windows 7, type "Mouse" in the Start Menu's search field and press ENTER. Here's one example of how to find the specific location of the setting. Note that this will differ depending on model. On the "Advanced" tab, click "Advanced feature settings." In the "Advanced feature settings" window that opens, switch to the "Touch Pad" tab. Then, check "Disable tapping" in the "Operations during key input" box or click "Settings" and uncheck "Enable tapping" in the "Tapping" box.

For information regarding issues specific to your model please check the web for Technical Support Bulletins.

In addition, it's been suggested that some third-party, non-Toshiba AC adaptors have been known to cause this problem. To see if it's related, unplug the AC adaptor when the mouse is exhibiting these symptoms. If the AC adaptor is the cause, unplugging it should resolve the issue. In addition, the mouse might behave normally once the laptop has finished charging. To avoid this, don't use third-party AC adaptors. Only use the official Toshiba AC adaptor designed for the laptop.