No. I'd send a message to support for an explanation if it's number way out of the norm. I had one once (it wasn't my entire balance by any means but it was a larger-than-usual amount) and was told it was because an advertiser was doing something against TOS.
Unless I misunderstand the question, this is what I normally see (and am seeing now) in the control panel. I believe it is simply the interim period between when the previous months payment is made (balance cleared minus deductions) and final earrings for the current month are posted (new balance established).
Prior to the actual end of the current month, they don't technically owe anything so the balance is zero or a bit less. This usually only lasts 5-7 days.