The 67-year-old said on Twitter that his symptoms were mild and that he was "optimistic" following the diagnosis.
The development comes as Mexico grapples with an upsurge in infections, with deaths nearing 150,000.
Mr López Obrador says he will continue working from home, including speaking to President Vladimir Putin about acquiring a Russian-made vaccine.
It was announced earlier on Sunday that a call between the two leaders will take place on Monday to discuss their bilateral relationship and the possible supply of Sputnik V jabs.
