No, you are not eligible. The eligibility conditions require for JEE Main Exam is the candidate must have passed 12th exam
and need to complete 12th standard with Physics, Chemistry and Mathematics as the subjects. Those who have completed diploma course are not eligible because diploma in Engineering is done after completing the 10th standard.
You can check out the complete details of the JEE Main Exam by Visiting Eduncle. Type JEE Main- Eduncle and click on the link.