There are several volcanoes on Mars, including Olympus Mons, the largest volcano in the solar system, the volcanoes on the Tharsis bulge,... But they are all thought to be inactive now.
When did the last volcano erupt on Mars?
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Berman and Hartman (2002) dated some lava flows of the Athabasca–Marte Valles system at < 20 Ma (mega-annum). Later, Vaucher et al. (2009) dated lava flows of the same region, finding ages even younger in some cases (around 2.5 Ma). In both studies the age estimates are derived from surface morphology (i.e., crater counts).
In Volcanoes: Global Perspectives, Lockwood & Hazlett go even further (emphasis mine):
Unlike Earth’s Moon, volcanic activity may be far from over on Mars. Detailed photographic studies by NASA’s Global Surveyor starting in 1997, and the Mars Express High Resolution Stereo Camera, which began orbiting Mars in December of 2003, provide evidence of effusive volcanism perhaps as young as 2–2.5 million years, with flows mantling the flanks of Olympus Mons erupted mostly within the past 200 million years. It cannot be assumed that Mars is now internally cold and volcanically dead, and in fact, volatile efflux may still be in progress.
Per this article, the most recent volcanic activity on Mars might be less than 1 million (Earth) years old. Pyroclastic deposits in Elysium Planitia were dated thanks to impact craters and were found to be very young.