Former lawmaker Phyo Zeya Thaw, writer and activist Ko Jimmy, Hla Myo Aung and Aung Thura Zaw were accused of committing “terror acts”.
The executions, which were first announced by the military in June, drew international condemnation.
They come in the wake of a 2021 military coup.
The junta overthrew the democratically elected government led by Aung San Suu Kyi’s National League for Democracy (NLD) in February last year, sparking huge protests which were swiftly crushed.
The shadow National Unity Government of Myanmar (NUG), which was formed in opposition to the coup, condemned the killings, saying they were “extremely shocked and saddened”.
It comprises pro-democracy figures, representatives of armed ethnic groups and members of the NLD. They urged the international community to “punish (the) murderous military junta for their cruelty and killings”.
The state news outlet – Global News Light of Myanmar – said the four men were executed as they “gave directives, made arrangements and committed conspiracies for brutal and inhumane terror acts”.
It said they had been charged under the counter terrorism laws, but did not say when or how they were executed.
The executions are the first since 1988, according to the United Nations. Previous executions in Myanmar have been by hanging.
Family members of the four men are waiting at Yangon’s Insein Prison to question authorities, according to BBC Burmese.
They were yet to receive the bodies, Ko Jimmy’s sister told the BBC.
Phyo’s wife, Thazin Nyunt Aung, said she had not been informed of her husband’s execution, Reuters reported. The families have all submitted applications for information on the executions.
The four men were handed the death sentence in January following closed-door trials that human rights groups have criticised as being unjust and non-transparent. Phyo Zeya Tha and Kyaw Min Yu, also known as Ko Jimmy, lost their appeals against their sentences in June.
Ko Jimmy, 53, was a veteran of the 88 Generation Students Group – a Burmese pro-democracy movement known for their activism against the country’s military junta in the 1988 student uprisings. He served multiple stints in prison for his involvement in the pro-democracy movement, before being released in 2012.
He was arrested in October last year after being accused of hiding weapons and ammunition at an apartment in Yangon and being an “advisor” to the National Unity Government.
Phyo Zeya Thaw, 41, was a former NLD lawmaker and a close ally of Suu Kyi.
A former hip-hop artist, he often drew the ire of the junta for his anti-military lyrics. He was arrested in November for alleged anti-terror offences.
Less is known about the two other activists – Hla Myo Aung and Aung Thura Zaw. They were sentenced to death for killing a woman who was an alleged informer for the junta.
United Nations Secretary-General Antonio Guterres had called the military’s decision to sentence the four activists to death “a blatant violation to the right to life, liberty and security of person”.
Military authorities have intensified their crackdown on local militias, opposition activists and those deemed to be harbouring anti-coup sentiments since they seized power last year.
They claimed the results of a general election that saw Suu Kyi’s political party winning by a landslide were rigged – an accusation election commission officials denied, saying there was no evidence of fraud.
Since the coup, Suu Kyi has been detained under house arrest, and slapped with a litany of charges ranging from corruption to violating the country’s official secrets act, which could see her serving a sentence of up to 150 years.
The Assistance Association for Political Prisoners (AAPP), which keeps a toll of those killed, jailed or detained by the military, says that 14,847 people have been arrested since the coup, with an estimated 2114 having been killed by military forces.