There used to be a Go-Kart facility on the right hand side of the main road on the way from the airport in to Muscat, closer to the airport than to town.
There was a tarmac on-road RC track there along with BMX tracks and of course the Go-Kart track.
However, that was a long time ago......
Let me know if you find out that it's still there.
Martin
Found it here;
http://www.kartingasia.com/kart_trac...rack-t151.html
The RC part is smaller than I remember (behind the 'grand' stand for the kart track), so probably worth looking elsewhere...