About 100 people took part in demonstrations across Nairobi on Tuesday.
Many Kenyans have been angered by a fresh wave of alleged police abuses carried out while enforcing coronavirus-related restrictions.
"We are not armed, and we just wanted to take our petition very peacefully, but as you can see they are very armed, they have arrested some of us, and they have injured some of us," protester David Oluoch said.
Nairobi-area police boss Philip Ndolo said nearly 30 people were arrested and that protesters had not been "observing distance" for the coronavirus pandemic.
"It's dangerous to hold such meetings now," he said.A protest organiser said 56 people were arrested.
Human rights activists said at least 22 people, including a 13-year-old boy, have been killed by officers enforcing the virus restrictions.
But activists said there has been no groundswell of widespread public protest in Kenya, one of Africa's biggest economies, that has been seen in other parts of the world.
For two decades, Kenya's police force has been ranked as the country's most corrupt institution
It is also the most deadly, human rights groups said.
Protest coordinator Gacheke Gachihi said social justice groups from 16 slums organised Tuesday's event to mark 30 years since opposition politicians protested to demand democratic reforms from the single-party regime at the time.
