Hi Dear,

Yes, you are eligible for JEE mains exam if you have completed your diploma  from an AICTE approved Institution of at least three years duration.

For more details you can visit the following link:

https://engineering.careers360.com/articles/jee-main-eligibility-criteria

Hope this helps.. Good Luck

hey,

after doing your diploma in engineering you are eligible to appear for JEE mains exam but there is a condition for diploma holders that is you are required to clear the both JEE mains and JEE advanced in order to get in IIT that too with no lateral entry, after qualifying your JEE mains exam you wont be facilitate to get admission in NIT , you need to clear JEE advance too.

hope this helps!