Fold top pair and move on? Level 5 blinds battle

[outofstep]

Sorry but Pokertracker has been acting wierd, no uploading HHs.

6 Handed 30+3 75/150

Folded to me in SB with 1600 chips. I have Q9s and raise to 400. BB Calls.

Flop: Q 5 8 rainbow.

I bet 400 and BB goes allin. He has me covered by 200 chips or so. BB seems like a decent player. Wasn't sure if he was making a move or he has a better hand. What would you do here?