Are you sure you got your numbers the right way around? What you've said implies it's turbo boosting (current clock speed above maximum clock speed), but i3's don't do that.
If you've got the the wrong way around, then it's down-clocked due to it idling (or thermal throttling, but given the amount, that is unlikely). This would be a power saving feature, which you can disable in the BIOS (although there's little point - as soon as you put load on it, it'll spin back up - my i7-4790K bounces between 800MHz and 4.52GHz pretty freely).