A 66-year-old woman allegedly attempted to drug two occupants of a Ballajura house before she set fire to the building.
About 6.50pm on November 11, police and Department of Fire and Emergency Services members were called to a house fire on Vista Parade.
A 79-year-old man, 66-year-old woman and 45-year-old man were found with minor burns and smoke inhalation.
Arson squad detectives arrested the 66-year-old after investigations and will allege she attempted to drug the others before lighting the fire.
She is set to appear before the Perth Magistrates Court today.