Hii!
Yes, you can definitely go for law courses after completing class 12th with science stream. The eligibility criteria for the course states that the candidate must have passed class 12th with minimum 50% to 60%  marks  in any relevant subject discipline from a recognised board of education. So, you can go for BA LLB after completing class 12th with science stream If you score as per the eligibility criteria.
Hope this helps.
Good luck!