Yes, well its surface is. One surprise from Curiosity is that it is a very thin surface layer.
Red Planet Mars Not So Red Inside
There is almost no oxygen in its present day atmosphere. But in the past it may have been oxygen rich. But doesn't necessarily mean there was life there in the past. The atmosphere could be oxygen rich through the effect of the solar wind stripping the hydrogen from water vapour and leaving oxygen behind.
One scientist thinks this might be how Mars got its red surface. Early Mars atmosphere 'oxygen-rich' before Earth's - BBC News
See also their press release: Mars had oxygen-rich atmosphere 4000m years ago
Another possibility is that other chemical processes oxidised the surface not involving free oxygen.
At any rate the surface is highly oxygenated now. Not just the iron oxides - which cover the rocks and make up the main component of the fine dust. Also all the salts (combination of an acid and a base) on Mars are highly oxygenated.
On Earth we have mainly chlorides (table salt), sulfides etc. On Mars the salts are nearly all sulfates, chlorates, and perchlorates, all highly oxygenated.
Which on the face of it is surprising since its atmosphere is almost entirely CO2, while Earth's atmosphere has large quantities of oxygen - you'd expect it to be the other way around that Mars had the reduced salts and Earth the chlorates and perchlorates.
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