The Non-Return-to-Zero On-Off Keying (NRZ-OOK) signal transmission is demonstrated indoors with a 74 GHz local oscillator and a pair of rectangular horn antenna. The BER performance of the system is researched with various transmission distances and bit rates. The results show that the performance decreases with the increasing of distance and bit rate. Error free transmission can be realized within 3.6 m for 5 Gbit/s and 6 Gbit/s signals with Forward Error Code(FEC), while just 2.4 m transmission can be realized for 7 Gbit/s signal.