The latest explosion was outside a mosque in Colombo's commercial area of Pettah, police said, adding that two people were taken to hospital.
Colombo National Hospital director Prasad Ariyawansa said two people admitted following the blast had minor injuries.
Two vehicles were damaged while shop windows in the area were shattered, police said.
There was no immediate claim of responsibility but the government blamed Friday's attack on a suicide bomber from the Tamil Tiger separatist group which lost its main political base in the island's north on Friday.
Police said Friday's bomber had tried to enter the air force base in Colombo but was stopped by sentries.
Suicide bombings are a trademark of Tamil Tiger rebels who were accused of a similar attack on Sunday in which eight people died.
The rebels have been fighting since 1972 for a state for ethnic minority Tamils separate from the majority Sinhalese community.