Yes it is okay if you keep your beard while appearing for NEET. 

Though candidates appearing for NEET have been given a prescribed dress code by NTA and it has been mentioned in the official brochure too. Candidates are also required to mention in the NEET application form whether they intend to follow the dress code of NEET 2019 as prescribed. Students appearing for the exam have been asked to adhere to a certain dress code that mentions the clothes, footwear worn by students on the day of the exam and other accessories that go with the dress worn on the day like jewellery, belts, caps etc.

Https://www.google.com/amp/s/medicine.careers360.com/articles/neet-dress-code/amp

I hope all your doubts have been cleared. Thank you.