In a metallic bond the electron orbitals that are hybridised to create the bonding orbitals include orbitals that do not contain electrons. This means that the bonding orbitals each contain on average less than 2 electrons (as opposed to in a normal covalent bond). There is still a balance in the average number of electrons around each atom and its protons so there is no net electrostatic charge.

The effect of this is that as the empty orbitals are basically at the same energy level as the populated ones it is possible for the electrons in these orbitals to move from orbital to orbital (and atom to atom) with little expenditure of energy. This is easy movement of electrons allows the material to conduct electricity.