I'm arriving into Frankfurt on QF and then have a layover for 3 hrs before a connecting flight on Czech Airlines to Prague.

I'm arriving into Frankfurt on QF and then have a layover for 3 hrs before a connecting flight on Czech Airlines to Prague. Is there a OneWorld arrivals lounge that I can utilise in Frankfurt during the wait?

There is no arrivals lounge in Frankfurt.  You would not be able to access any Oneworld Lounge when travelling on Czech Airlines as you are not departing on a flight operated or marketed by a Oneworld Alliance member.

I'm not really sure on Frankfurt's airport, but I think there is a airberlin lounge in the domestic terminal?

As driley28 says, no oneworld arrival lounge.  If you are a member of an FFP that gives you access even when you are flying non-oneworld (such as a CX Diamond member) then you may be able to use that airline's own lounge, if they have one (incidentally, the CX lounge in Frankfurt is very nice, with decent showers).  Are you on a premium ticket on Czech Airlines or a member of a Skyteam FFP?  If so, you might be able to access a Skyteam departure lounge (for a list, look here http://www.skyteam.com/en/your-trip/Journey-Information/Lounge-Finder/Skyteam-lounges-in-Frankfurt-Frankfurt-International-Airport/).  If you are not a Skyteam FFP and flying economy, all is not lost - you can buy your way into Skyteam's Sky Lounge for 30 euros for 3 hours, and that also has showers - but I haven't visited it, so can't comment on the lounge itself.