Two possibilities come to mind.
1: Your palm is resting on the trackpad, causing the cursor to jump, and you have overtype mode on
2: You need a new keyboard
I am using a Lenovo laptop with Win 7. However, lately my keyboard is acting up. It
tends to delete (backspace, to be clearer) characters I type (at
random). And, I need to press that key more than a couple of times to
get that character in.
Not sure what the issue is.