This paper presents the design of a frequency reconfigurable folded dipole antenna for terahertz photomixers. The proposed folded antenna can operate at two different frequencies, namely 330 GHz and 590 GHz, increasing the radiation efficiency at both frequencies. The reconfiguration of the antenna is achieved by means of Nano-Electro-Mechanical Systems (NEMS) switches. The proposed antenna has a radiation resistance of 465 Omega and 216 Omega, providing an improvement by a factor 2.2 and 2 at 330 and 590 GHz, respectively. To the best of our knowledge, this is the first demonstration of NEMS reconfigurable folded antenna for terahertz photomixers.