Is it “a MA” or “an MA” degree? Which is correct?

“An MA” is correct because the “m” in “MA” is pronounced “em”. “Em” is a vowel sound so we need to use “an”.

I have an MA degree in Science. 

The rule of whether you use “a” or “an” depends on if there is a vowel or consonant sound at the beginning of the next word.

We usually use “an” with words that start with vowels but in this case, we have an acronym that begins with the letter “M”. The letter “M” is pronounced as “em” so it begins with a vowel sound.

We use “an” before words(or in this case a letter) that start with a vowel sound.

You can learn more about “a” and “an” before acronyms here.