"Why are you afraid now?"
Here's the breakdown:
* mbeirimid - a shortened form of "an bhfuil eagla ort" (are you afraid)
* beo - means "alive" or "living" and is used here to emphasize the state of being afraid
* ar an am seo - means "now" or "at this time"
The phrase could be translated more literally as "Why are you alive and afraid now?", but it's commonly understood as simply meaning "Why are you afraid now?".
Let me know if you have any other Irish phrases you'd like to understand!