Yes, it's a very common german surname,
Some variations:
KUNZ, KÜNZ, KUENZ, KUNZE, KÜNZE, KUENZE
and the same again, with TZ
KUNTZ, KÜNTZ, KUENTZ, KUNTZE, KÜNTZE, KUENTZE
The original german name could have been any of the above, now 'anglicised' to KUNTZ, to keep the german proninciation.
It is pronounced KOUNTZ (as in SHOULD) and not KUNTZ (as in CUP)
Bob