The robbery happened at 10 a.m. Thursday in the 100 block of Pine Tree Road.
According to police, the man approached two workers at a house demanding cash.
He was last seen running southbound on Pine Tree Road, toward King of Prussia Road.
Lockdowns were announced shortly after 10 a.m. at Cabrini College, Eastern University and Archbishop Carroll High School.
Eastern University sent a text alert to students announcing the campus was on lockdown.
Cabrini College posted the following information:
EMERGENCY NOTICE: The campus is on lockdown because of an off-site incident.
The Radnor Police Department has requested that campuses in the area lockdown as a precaution.
Please stay in your rooms and offices.
If you are outside, please seek immediate shelter in one of the buildings.
If you are on your way to campus, please do not come to campus until you receive notice that the lockdown has ended.
We are working with Radnor Police Department to ensure the safety of our community.
Final Exams: The final exam scheduled for 11:00AM today has been moved to 11:30AM today.
If the lockdown has not been resolved in time for the 11:30AM exam, we will send further instructions.
At 11:15 a.m. Action News was told Radnor Township Police had determined there was no longer a potential threat, and the lockdowns at all three schools had been lifted.
Anyone with information is asked to contact Radnor Township Police at 610-688-0503.