Is it true that only B.Tech students can do MBA in NIT?

For pursuing MBA in NIT, it is not necessary that you should be graduate in B.tech. Normal graduate students can pursue MBA from the NITs. Only the minimum eligibility criteria for 50 or 60% in graduation should be fulfilled.

No. that's a myth. b.tech students can do MBA from nit. but that does not mean they are the only ones selected. Rather NIT looks for varied background in their classes.

for MBA in NIT you need to have a background of engineering or math in 12th standard