Is a student who has done a Diploma in mechanical having 6-years of experience eligible for distance MBA/PGDM course?

Dear Satyam! Having just Diploma is not enough for getting admission for MBA/PGDM. You have sufficient (very good) years of work experience. So my suggestion is that you just now do Bachelors (if you are in age limit). And prepare very hard for CAT-GMAT and MAT. This will surely maximise your chance