Monday’s blast hit the village of Nguetchewe in Cameroon’s far north region, in an area near the border with Nigeria regularly targeted by Boko Haram jihadists.
"The toll of this attack is four dead and two injured," the source, who was at the scene of the attack, told AFP.
A source close to regional authorities confirmed that a deadly attack had taken place in Nguetchewe, but was unable to provide details.
The security source said the attack took place around 6.00am (5.00 GMT) just as morning prayers were ending.
"The suicide bomber, a young boy, arrived in the village by foot," the source said, adding that a witness had noticed his behaviour seemed suspicious and had tried to intercept him.
"The bomber ran towards the mosque, where he set off the explosives he was carrying with him." Cameroonian troops were at the scene of the attack, the source said.
It is the second deadly blast to hit the Far North in less than a week, following a bombing at a mosque in Kolofata district during morning prayers last Wednesday.
In November 2013, French priest Georges Vandenbeusch was kidnapped from Nguetchewe, with the Boko Haram Islamist group claiming responsibility. He was freed after about 50 days in captivity.
Communications Minister Issa Tchiroma Bakary said on Friday that nearly 1,200 people had been killed in the Far North since 2013, when Boko Haram began attacking Cameroonian territory bordering its northeast Nigerian stronghold. Cameroon boosted its military presence along the Nigerian border in 2013, under increasing pressure from the jihadists on the other side of the border.
Boko Haram, which has waged a six-year campaign for a hardline Islamic state in northeast Nigeria, has been using the Far North as a base for supplying weapons, vehicles and equipment.
Along with Nigeria, Niger, Chad and Benin, Cameroon is part of a regional military force fighting the jihadists, who have killed at least 17,000 people and made more than 2.6 million others homeless.