The incident took place at around 2.45pm on Thursday at Sir John Talbot's School in Whitchurch.
While police assessed the situation, the school was given advice to implement its 'lockdown' procedures, in which students were kept in their classrooms with members of staff.
The lockdown lasted for approximately 10 minutes, after which students were then able to leave school.
Police confirmed they did not discover any weapon following investigations and they are still working to identify the individual concerned.
Jeremy Layton, communications officer for West Mercia Police said: "At around 2.45pm on February 2, police received a report of a person with a weapon near to the Sir John Talbot Upper School, Prees Road, Whitchurch.
"The person was described as being dressed in black clothing. No one was threatened with a weapon.
"This is being treated as an isolated incident and no identified risks have become apparent to any of the children at the school.
"Police are continuing to make enquiries to identify the person."
In a message to parents, headteacher Tim Stonall said: "You may be aware that close to the end of the school day, we were notified by the Police of a possible incident in the locality. Whilst they assessed the situation, advice was given for the school to implement its 'lockdown' procedures.
"This meant that students were kept safely in their classrooms with a member of staff.
"Once the Police had assessed the situation, they notified us quickly and confirmed that we could end the 'lockdown' after approximately ten minutes. Students were then able to depart safely from school
"We apologise for an inconvenience this short delay may have caused. However, in the interest of keeping staff and students safe, we will always act on the advice given to us by the emergency services.
"Thank you for your understanding."