Yes, You can pursue MS in CS after doing BSc and a post graduate diploma course.

Most of the Post graduate Universities in the CS require you to have completed at least 16 years of education before you can apply for an MS course. These 16 years are broken up into

10 + 2 + 4 = 16 [years of education]

But in your case, you have a 3 year BSc course and a 1 year diploma program.
So, that is...

10 + 2 + 3 + 1 = 16 [years of education]

Which also satisfies the 16 year rule. So you are good to go. You can apply for MS without hesitation.

For 3 year graduation courses, an extra 1 year of education has to be added to be eligible for MS in US.