Sir I have passed 12th bio with 78 percent marks in CBSE board. But I have got admission to diploma in Electrical Engineering (AMU).

Hello dear student,
Greetings,
I will suggest you to completely focus on neet if you really want to become a doctor as neet is not that easy,  it's a tough nut to crack due to large number of aspirants and very limited number of seats. So in order to crack neet you will have to completely focus on it which you will not be able to do if you do your neet preparation along with your diploma.
So , I want you to take some time and make a wise decision.
Thankyou

Hello student yes you can appear in neet 2020 as eligibility for Neet is NEET 2020 Eligibility Criteria  Do you think you're allowed in the Exam?
ParametersNTA NEET 2020 Eligibility Criteria - Complete Detail
Qualifying Exam10+2 or equivalent from a recognized board.
Minimum Age Requirement17 years as on December 31, 2020.
Maximum Age Limit25 years (UR), 30 years (OBC/SC/ST/PwD).

Feel free to comment if you have any doubt
Good luck