Previous studies on the anomalous Hall effect in coplanar noncollinear antiferromagnets are revisited and extended to magneto-optic properties, namely magneto-optic Kerr effect (MOKE) and x-ray magnetic dichroism (XMCD). Starting from group-theoretical considerations the shape of the frequency-dependent conductivity tensor for various actual and hypothetical spin configurations in cubic and hexagonal Mn3X compounds is determined. Calculated MOKE and x-ray dichroism spectra are used to confirm these findings and to give estimates of the size of the effects. For Mn3IrPt and Mn3PtRh alloys the concentration dependence of the anomalous and spin Hall conductivity is studied in addition.