The group’s coordinator Carbone Beni and three of his colleagues were released from Kinshasa’s Makal prison, the UN-founded radio station Okapi said.
They had been arrested on December 30, 2017, after calling for a protest march against President Joseph Kabila.
In September, they were sentenced to one year in prison for “offending the head of state”, among other charges.
Before the verdict, they were held at a hidden location for several months.
Another opposition movement, Fight for Change (Lucha) welcomed their liberation Tuesday, calling their sentence “unjust” and having been ordered by Kabila.
“Prison doesn’t weaken us, on the contrary, it makes us stronger,” Lucha said.
Presidential, legislative and provincial elections were due to have been held last Sunday, defusing a two-year-old crisis over the future of Kabila.
But national election supervisors ordered a week-long postponement, blaming a warehouse fire that destroyed voting machines and ballot papers earmarked for Kinshasa.
Opposition candidates are concerned over the use of the electronic voting machines, which they fear will allow massive fraud. Electoral authorities say the machines will make the ballot more efficient.
On Tuesday, several opposition candidates urged mobile telephone operators in the country to disable any SIM cards used in the machines they believe will allow officials to transmit vote results from the machines before a manual count.
The terminals have a touch screen for voters to click on their preferred candidate.
After the election postponement, Filimbi released a statement calling for the population to mobilise against “the electoral sham put in place by the Kabila regime”.