Hello,


No, Biology isn't compulsory.
NEST Eligibility Criteria 2019 - Academic Qualification
General and OBC candidates must have completed their Class 12 qualifying examination with minimum 60 percent aggregate from a recognized board. Candidates from the SC/ ST categories must secure minimum 55 percent aggregate in their class 12 qualifying examination.
Candidates who apply must have passed the qualifying examination in 2017 or 2018. Candidates who appear for their qualifying examination in 2018 are also eligible to apply.
NEST Eligibility Criteria 2019 - Age Limit
Candidates who apply must be born on or after August 1999. The age limit for SC/ST candidates will be relaxed upto 5 years.
Candidates belonging to the reserved category need to submit their reservation eligibility certificates only during the admission counselling process.

https://university.careers360.com/articles/nest-eligibility-criteria

I hope this help.