keyboard typing after I initiate first character and is wrong ?

using blue tooth keyboard on mac mini with el capitan.

I type in my password, it takes over and keeps auto filling and is too many characters and doesn't sign me in. I can't restart or shutdown correctly because it just keeps doing the same thing, Its like a circuit, won't stop. So I turn off computer with power button, turn it back on in 10 minutes and it works fine. this has happened 3 or 4 times recently. any idea what it is?