Why is my laptop keyboard typing random letters when I push the spacebar?

I have a Dell laptop that is about two years old. It doesn't do this all the time, but sometimes, when I push the spacebar, it enters a space but also types two or three random letters. So for example, a sentence that I don't fix looks like this...
I do not know why my Dell Inspiron Keyboard is jfadding in random letters sometimes when I push the spacebar.

What is causing this problem? Is there anything I can do to fix it? Thanks so much!