Can I pursue MBA after completing class 12th from science stream?

Yes, you can go for integrated MBA in which you will learn BBA+MBA (5-year course). If you want to do MBA then go for it, otherwise do Bachelor's and then MBA because you can change your stream in between the courses.

You need to be a graduate to pursue MBA. It doesn't matter which stream did you opt for in class 12th. You need to score a minimum of 50 percent marks in graduation for the same.

MBA being a Master's degree can only be done after obtaining a Bachelor's degree. Concentrate on your Bachelor's degree at the moment.

MBA is a two-year post-graduate degree course. There are four semesters in MBA. Minimum eligibility: Graduation (3 years) or equivalent qualification from a recognised university. You should appear for at least CAT or MAT examination as these examinations are accepted by most of the colleges.