The victims were identified as two women, aged 25 and 27, and a 26-year-old man. Firefighters found their bodies inside an apartment on the building's second floor.
The five injured people suffered from smoke inhalation and were taken to hospitals in Bochum for treatment. Their nationalities have not been disclosed in media reports.
41-year-old man arrested
Police have arrested a 41-year-old Romanian national who also lived in the building on suspicion of murder in connection with the incident.
Authorities have not provided further details about the circumstances surrounding the fire or the suspected motive.
Fire breaks out in Bochum's Hofstede district
The incident occurred early Tuesday at a multi-family residential building in the Hofstede district of Bochum.
Emergency services responded to the blaze, but three residents were found dead inside the apartment.
An investigation is underway to establish the circumstances of the fire and the events leading up to the deaths.
The incident has claimed the lives of three young Indian nationals, while five other people were hospitalised following the blaze.