The high school in Arras, northern France, where a teacher was fatally stabbed on Friday was evacuated on Monday morning following a bomb alert, a Reuters photographer on site saw.
A police explosives expert team arrived on site.
Teachers and students of the Lycee Gambetta high school gathered in the courtyard of a building opposite their school, as civil protection personnel comforted them.
A 20-year-old man fatally stabbed a French teacher and wounded two other people in an attack on Friday at Lycee Gambetta in an attack that President Emmanuel Macron condemned as "barbaric Islamic terrorism."
France was put on its highest security alert following the attack.