  We report coherent spin manipulation on Cr$^{5+}$ (\emph{S} = 1/2, \emph{I} =
0) doped K$_3$NbO$_8$, which constitutes a dilute two-level model relevant for
use as a spin qubit. Rabi oscillations are observed for the first time in a
spin system based on transition metal oxides up to room temperature. At liquid
helium temperature the phase coherence relaxation time \emph{$T_2$} reaches
$\sim 10$ $\mu$s and, with a Rabi frequency of 20 MHz, yields a single qubit
figure of merit \emph{$Q_M$} of about 500. This shows that a diluted ensemble
of Cr$^{5+}$ (\emph{S} = 1/2) doped K$_3$NbO$_8$ is a potential candidate for
solid-state quantum information processing.
