There is no Prime B450a, there is a PLUS though, is that the one you mean? We need to know the exact model. Also we need to know the exact model of DIMMS (the ram) too.
But you can always check yourself on the QVL (Qualified vendor list) on Asus website. in this case: https://www.asus.com/Motherboards/PRIME-B450-PLUS/HelpDesk_QVL/