SeF6 is not polar. Although the Se-F bond is polar, the SeF6 molecule has an octahedral coordination symmetry, and the net dipole moment due to the six polar Se-F bonds is zero.
A polar molecule has a net dipole moment. In order to determine whether a molecule is polar, the valence shell electron pair repulsion rules should first be used to identify the three-dimensional geometry of the molecule. Then, the net dipole moment due to the polar bonds in the molecule should be determined. These bonds often have atoms of different electronegativities on their two ends. For example, selenium has an electronegativity of about 2.55, while fluorine has an electronegativity of about 3.98.