If it's just registration and not activation, then then is nothing to worry, about since registration is optional and shouldn't affect the use of pse 6.
Sometimes though, the registration dialog will keep popping up, so if that's the case we just need to know what operating system your using so we can tell you how to stop it.
If you registered while using on another computer, then there wouldn't be any need anyway.
If you have never registered pse 6 and still want to, you can sign into your adobe account and in the My Products and services section, use Register new products.