Kenyan human rights activist Boniface Mwangi, who has played a prominent role in anti-government protests, was freed on bail on Monday after being charged with possession of teargas canisters and a single rifle round found in his home.

Kenyan activists have been on edge over the arrests of government critics since a political blogger died in custody in June, triggering weeks of violent demonstrations in which around 50 people were killed.

Police had arrested Mwangi, 42, on Saturday and said they had recovered unused teargas canisters, a "7.62mm blank round", two mobile phones, a laptop and notebooks.

Mwangi was "found in possession of noxious substances to wit three teargas canisters without lawful authority," according to a charge sheet seen by Reuters. He was also accused of illegal possession of a single round of blank ammunition.

The courtroom was packed with hundreds of activists, some wearing Kenyan flags.

"They have no evidence," Mwangi told reporters, describing his prosecution as "a big shame".

His lawyer told Reuters he was grateful to the court for agreeing to release Mwangi on bail.

Mwangi, who once ran for parliament on an anti-corruption platform, has earned a reputation for speaking out against human rights violations in Kenya and abroad.

He was expelled from neighbouring Tanzania in May, where he had travelled to observe a hearing in a treason case against an opposition figure.

Last month, hundreds of Kenyans took to the streets to protest against the death in police custody of political blogger Albert Ojwang.

Police initially implied that Ojwang had died by suicide, but later apologised after an autopsy found that his injuries pointed to assault as the cause of death.

The demonstrations over Ojwang's death reignited protests that had erupted last year over the cost of living and alleged police brutality and corruption.