It remains unclear whether he will also face terrorism-related charges as earlier suggested by the Directorate of Criminal Investigations (DCI).
On Sunday, the DCI had claimed that Mwangi was being held in connection with the facilitation of terrorist activities.
Mwangi was arrested on Saturday at his home in Lukenya, Machakos County, and spent two nights in custody at the Pangani Police Station.
His arrest has sparked widespread condemnation from civil society groups and legal experts, who accuse the government of misusing anti-terrorism laws to suppress peaceful dissent.