mostly, yes. people tend to focus their masters on some area that their bachelors was about. a bachelors (~120 credit hours classroom instruction) is about giving the student a familiarity with many aspects of a broad topic. the masters is about giving a student familiarity with how to conduct specialized research on a narrower area within a broad topic. theres a lot less classroom instruction in a masters (~30 credit hours) program and more time pursuing specialized research. a BS in math says i know a lot about math. an MS in math says i conducted specialized research in a math area.

a prospective masters student is not required to not get an MS in the same area their BS was in. its just uncommon because its difficult, since a student has to apply for a masters program. you could, for argument's sake, have a BS in math and then decide to get an MA in art history.

the people running the graduate level art history program would approve you assuming you met the requirements of the program, but you would likely have to take some bachelor's level classes (as a "post baccalaureate" student) that students with a BA in art history would have taken before you could officially enter the program, as well as maybe an entrance exam of some kind to show basic proficiency in language, etc.

and they would definitely want to interview you and ask about your interest, what you want to research in art history and how you might be able to leverage your knowledge and training in math (if possible).

this theoretical person would be "multi-disciplinary" and a bit if an oddball in the masters art history program, but if they satisfied the requirements for the MA program and were a good student with a plan for what they specifically wanted to research and found an art history faculty member who would act as their advisor, it could happen and likely make everyone else in the department curious as hell, intellectually, about what their specific research topic was. and likely, they might want you to find a math faculty to be on their committee (with the art people) when they defend their masters research (typically a long oral exam in front of a panel aka the committee) assuming it includes some math stuff.

my bachelors was in an individualized inter-/multi-/transdisciplinary field, so i was all over the place on campus across 3 colleges and several departments, so i learned how to have hot takes in a wide variety of disciplines. i had wanted to keep some of that straddling-two-fields vibe with my MS, but ultimately it was too much of a hassle to wrangle in a tight window (i was also working full time).

its more common in PhDs, where a committee is larger and you get 5 years to put it all together instead of 2 like an MS.

so i just picked a narrow area i was most interested in, and did that.

i went to a dissertation defence of a multi-disciplinary PhD and it was amazing to watch the absolute inability of some of the faculty committee to grapple intellectually with very basic shit outside their area of expertise, while others were absolutely thrilled to learn new things and found the project very engaging.

truly, academia is a land of contrasts.