Cubase records ambient noise even tho no mic is plugged in!

I am attempting to record audio from my Yamaha MX 88 . For some reason, Cubase is also picking up ambient sounds , evenm though no microphone is plugged in. Is there something I have to disable on my laptop? Please help me! Thanx Bruce in Dorset

More info is required here Bruce.

What audio interface do you have selected, is it possible you have a mic coming in to the MX88?