In the presence of a magnetic field the frequency dependences of the symmetrical ( sigma _xx) and anti-symmetrical ( sigma _xy) parts of the phononless conductivity tensor in disordered systems with localised electronic states are calculated by the Kubo formula (1975). The region of not too low frequencies for which the phononless contribution to the conductivity predominates is investigated. Depending on the ratio between the parameters which characterise the system, the obtained results for Re sigma _xx( omega ) describe fairly well both the experimental data on the frequency dependence of the conductivity in amorphous semiconductors (coinciding with the well-known Mott expression on the low-frequency edge) and experimental data on absorption in doped and compensated semiconductors at low temperatures. Calculations show that the value of Re sigma _xy which is responsible for magnetic rotation is non-zero only in the frequency region where absorption exists. The curve of Re sigma _xy( omega ) undergoes a twofold sign inversion in the absorption band region.