One suicide bomber struck inside Badr mosque in southern Sanaa while another targeted worshippers as they fled outside, witnesses said.
The third suicide bomber targeted Al-Hashahush mosque in northern Sanaa.
Nashwan al-Atab, a member of the health ministry's operations committee, told AFP that 77 people were killed and 30 of the wounded were in critical condition.
The Huthi militia's Al-Massira television said hospitals in the capital had made urgent appeals for blood donations.
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Footage aired by Al-Massira showed bodies lying in pools of blood outside the mosques, as worshippers rushed the wounded to hospitals in pick-up trucks.
There was no immediate claim of responsibility.
Another suicide bomber blew himself up outside a mosque in the northern Huthi stronghold of Saada, a source close to the militia said.
Only the assailant was killed in that explosion and tight security at the mosque prevented the bomber from going inside, the source added.
The Huthis overran Sanaa in September and have since tightened their grip on power.
Yemen's top security body blamed Al-Qaeda for a car bomb in January that killed 40 people and wounded dozens more at a police academy in Sanaa as recruits lined up to register.
But a leader of the jihadist network denied responsibility at the time.
Al-Qaeda in the Arabian Peninsula (AQAP) is regarded by the United States as the extremist network's deadliest branch.
Yemen, a front line in the US war on Al-Qaeda, has descended into chaos since the 2012 ouster of longtime strongman Ali Abdullah Saleh, who has been accused of backing the Huthis.