Nope! After Diploma in Mechanical Engineering you can pursue BTech in Mechanical Engineering via Lateral entry examination but not in BSc-CS. For BSc you need to have passed 10+2 with Mathematics and Physics/ComputerScience/Statistics/Electronics. Now if you have joined diploma after 10 then you have to pursue 12 and if you have passed 12 and joined Diploma then you have to take admission in year 1 of BSc-CS course. BSc CS is a three year UG course.

To know more about Lateral entry examination visit the link below:

https://engineering.careers360.com/articles/what-btech-lateral-entry-eligibility

To know more about BSc CS visit the link below:

https://www.careers360.com/courses/b-sc-computer-science

I hope this answer helps. All the very best for your future endeavors!