No. Assuming this is GCSE, Spec A is linear (2 exams at the end of the course) Spec B is modular (3 exams spread through the course). Both are available at Foundation and Higher. The maths you need to know is the same. The option to take modular maths exams spread through the course is being withdrawn.
If it's IGCSE then the two specifications have quite distinct roots and while the ovelap between them is defintely huge, I don't know if there are any differences. Spec A is the more common/widely take one.