An active stand-off imaging system operating at 230–320 GHz is presented. Imaging is achieved by combining a line array consisting of 8 sources and 16 detectors with a scanning cylindrical mirror system. The stand-off distance is 8 meters and the effective aperture of the system is 0.5 meters by 0.5 meters. Range and intensity information of the object are obtained using an active FMCW (frequency modulated continuous wave) radar principle. Data acquisition time for one line is as short as 1 ms. Synthetic image reconstruction is achieved in real-time by an embedded GPU (Graphical Processing Unit). The data indicates a spatial resolution of about 2 cm and the range resolution of about 2 mm. To analyze the performance of the system, high-precision measurements employing a vector network analyzer are presented. An outlook on further developments is given.