Min 毋免: m̄-bián only, or possibly m̄-mián?
When pronouncing, both of them are okay since we can tell what (s)he says. But it is informal and incorrect to say mián. We know that /p/ in hokkien is same as b in chinese pinyin, and /b/ in hokkien sounds near /m/. Therefore, /b/ sometimes sounds like /m/. But it is wrong to pronounce or write /b/ as /m/. Pā-bián sounds like mián.