Hollway Road was cordoned off due to a “police incident”.
Cops were seen shouting “stand back” to all anxious pedestrians standing in the area.
London Overground tweeted: “No service between Highbury & Islington & Dalston Junction due to a security alert at Highbury & Islington.”
The bus involved in the incident was reportedly a 271 service to Moorgate.
Metropolitan Police have since confirmed the evacuation took place due to an abandoned suitcase on a bus.
Specialist officers examined it as a “precaution”.