A resident in the area told The Associated Press that the gunmen randomly opened fire on a street as Christians were celebrating a feast day. He spoke on condition of anonymity for fear of reprisals.
The state-run SANA news agency described the attack as a "massacre" and said that women and children were among the dead.
But activists said that many of those killed were pro-government militiamen manning checkpoints.
The Britain-based Syrian Observatory for Human Rights said that nine of those killed were Christians. It said rebels attacked checkpoints manned by the pro-government National Defense Forces militia, killing five of them. It said the other six were civilians, including two women.
Christians, who make up about 10 percent of Syria's population, say they are particularly vulnerable to the violence sweeping the country of 22 million people. They are fearful that Christians will be caught in the crossfire between rival Islamic groups.
Many rebels, who are mostly Sunnis, consider Christians to be supporters of President Bashar Assad's regime. The regime is dominated by members of Assad's minority Alawite sect, an offshoot of Shiite Islam, and members of some other religious minorities consider it a bulwark against extremists among the country's Sunni majority.
SANA said the attack occurred after midnight Saturday on a road linking the Christian villages of Ein al-Ajouz and Nasrah in Homs province.
The witness said many of the dead were refugees from the central city of Homs, which witnessed heavy clashes between rebels and troops over the past two years. Tens of thousands of Christians left downtown districts in Syria's third largest city because of the fighting.
Attacks against Christians have not been uncommon in Syria since the country's crisis began more than two years ago. Two bishops were abducted in rebel-held areas in April and an Italian Jesuit priest, Father Paolo Dall'Oglio, went missing last month while on a trip to the rebel-held northeastern city of Raqqa.
Unrest in Syria began in March 2011 and later exploded into a civil war. More than 100,000 people have been killed in the conflict.