Hey Kavita.

To be eligible to take the NDA entrance exam the eligibility criteria laid out states that you need to pass class 12th from a recognised board. And NIOS is a board which is recognised nationally. So if you have completed class 12th from NIOS with science subjects you seem to be eligble to take The NDA entrance exam as long as the other eligibility requirements like age, physical standards etc are fulfilled.

Best of luck