The given points are $0(0,0) \mathrm{A}(3, \sqrt{3})$ and $\mathrm{B}(3,-\sqrt{3})$.
$0 A=\sqrt{(3-0)^{2}+\{(\sqrt{3})-0\}^{2}}=\sqrt{(3)^{2}+(\sqrt{3})^{2}}=\sqrt{9+3}=\sqrt{12}=2 \sqrt{3}$ units
$\mathrm{AB}=\sqrt{(3-3)^{2}+(-\sqrt{3}-\sqrt{3})^{2}}=\sqrt{(0)+(2 \sqrt{3})^{2}}=\sqrt{4(3)}=\sqrt{12}=2 \sqrt{3}$ units
$0 B=\sqrt{(3-0)^{2}+(-\sqrt{3}-0)^{2}}=\sqrt{(3)^{2}+(\sqrt{3})^{2}}=\sqrt{9+3}=\sqrt{12}=2 \sqrt{3}$ units
Therefore, $O A=A B=0 B=2 \sqrt{3}$ units
Thus, the points $0(0,0) \mathrm{A}(3, \sqrt{3})$ and $\mathrm{B}(3,-\sqrt{3})$ are the vertices of an equilateral triangle
the area of the triangle $0 \mathrm{AB}=\frac{\sqrt{3}}{4} \times(\text { side })^{2}$
$=\frac{\sqrt{3}}{4} \times(2 \sqrt{3})^{2}$
$=\frac{\sqrt{3}}{4} \times 12$
$=3 \sqrt{3}$ square units.