The publication describes a mobile active heave compensator provided with an attachment device for suspending the compensator from a load bearing device and an attachment device for carrying a payload. The compensator comprises a passive heave compensation part and an active heave compensation part and is associated with a sensor arrangement producing input signals for a control unit and a power source. The compensator incorporates a hydraulic fluid pump and/or motor device, affecting the active heave compensating part, producing output signal(s) to the hydraulic fluid and/or motor device to transport the hydraulic fluid as required, based on input signals received from the sensor arrangement.