dear Sir/mam I get a call from doon business school but i didn't register for this after cat result, it come self, is it fake or it may be?

If you've received an email and the adress it was sent from contains their official extension then it won't be fake. In fact colleges like Doon Business School, Krupanidhi School of Management and many colleges of similar grade send emails to students for admissions as these are not much sought after colleges. You can definitely go for their interview once because this way you'll get some experience.

All the very best