The men were reportedly trying to broker talks between Sunni Muslims and members of the minority Alawite sect in the area when they were shot dead.
Two of the men were retired military officers, and another was an imam, according to a UK-based activist group report to BBC News.
President Bashar al-Assad's government is dominated by Alawites, while the uprising has been predominantly Sunni.
A video posted online by the UK-based Syrian Observatory for Human Rights purports to show the bodies of the six men and names them.
The Observatory said they were trying to set up talks in an area where fighting erupted last week.
They were killed near the Alawite village of Hajar al-Abyad, which the Observatory describes as a pro-Assad stronghold, and a centre for the "shabiha" (pro-regime militia) in the region.
Committees of mediators have been active in Homs and the surrounding areas. They have been set up mainly by local pro-regime figures with the aim of decreasing tension between Alawites and Sunni villagers.
Analysts say opponents of the regime have been sceptical toward the committees as they are sponsored by government, but they have reportedly had some success in resolving kidnap cases.
However, in this case, pro-regime militias began to suspect the mediators were secretly working with rebels, one resident told Reuters.
Most locals believed the team was killed with tacit approval from local government officials, the resident added.
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