The blast occurred when a building guard who was shimming the trees in the garden touched the device. Three of his family members and another man passing by accident were wounded.
There was no immediate claim of responsibility and the cause of the explosion was not immediately known.
Egypt has been battling wave of anti-security attacks, mostly centered in Sinai since the ouster of the Islamist leader Mohamed Morsi in 2013. Few attacks crept into the capital and other cities, Xinhua reported.