The active excitation of global Alfven modes using the JET saddle coils as the external antenna, will provide information on the damping of global modes without the need to drive the modes unstable. For the modelling of the Alfven mode excitation, the toroidal resistive MHD code CASTOR has been extended to calculate the response toan external antenna. The excitation of a high performance, high beta JET discharge is studied numerically. In particular, the influence of a finite pressure is investigated. Weakly damped low-n gobal modes do exist in the gaps in the continuous spectrum at high beta. A pressure driven global mode is found due to intercation of Alfven and slow modes. Its frequency scales solely with the plasma temperature, not like a pure Alfven mode with density and magnetic field.