NO you are not eligible as GATE is only for those candidates who have completed their graduation or in the last year of graduation.
If you are studying diploma then you can give entrance and join any degree college based on the subject you pursued in your diploma.
After completing your graduation or in the last year of graduation you can apply for GATE. In Mean-time, you have to practice well and give your best in the exam.
Hope it helps!
Feel free to comment if you have any doubt