It's only another quarter to call. My guess is that he missed his draw and is hoping a quarter bet will make you fold it...If he had a hand to beat you, he would have bet more than a quarter...a quarter bet is a...well, desparate attempt at making you fold...it would only cost you a quarter more to, at the least, find out what he was holding.

If he had raised you big(ie-a buck or more), perhaps he was trapping you...

At worst, you lose one more quarter to see what he's got...at best, you spend one more quarter and see what he's got and take the pot.