The Red Cross has suffered kidnappings of its staff in the past by jihadist groups.
"The four Malian workers of the ICRC (International Committee of the Red Cross) were released Monday afternoon by their kidnappers. No ransom was paid," the local official said Monday on condition of anonymity.
"They are all in good health".
According to another official who saw the workers after they were freed, "the fact that they are all originally from the region is what probably facilitated their release".
"Our colleagues abducted in the region of Mopti have just been set free without conditions," ICRC tweeted a little after 8pm (2000 GMT) Monday. "Thank you to all who supported us to make this happen".
The Red Cross, which had briefly suspended operations in the northern city of Kidal following a burglary at its offices last month, has suffered kidnappings of its staff in the past by jihadist groups.
In April 2016, three Red Cross workers were taken hostage by Islamist group Ansar Dine in northeastern Mali, but were released days later.
However it is unclear who exactly was behind this weekend's kidnapping.
A foreign security source in Mali's north said the two kidnappers claimed "extremist" ties. A Malian security source had previously told AFP that the kidnappers were "probably Islamists".
The workers targeted in the kidnapping were "conducting a survey of the humanitarian situation" on Sunday around 7 pm "when unidentified and armed individuals said they had to come with them," the Red Cross had posted on Facebook Sunday.
Armed men abducted five Malian workers, the Malian security source had said, including one woman who "was immediately let go".
Northern Mali fell to jihadist groups linked to Al-Qaeda in March 2012, and although these forces were driven out of key towns by a French-led military intervention the following year, the Islamists have now spread further south.
Three Malian jihadist groups with previous Al-Qaeda links recently joined forces to create the "Group to Support Islam and Muslims" (GSIM), led by Iyad Ag Ghaly of Ansar Dine, and have claimed several attacks against foreign and domestic forces.