The existence of (sub)micrometer scale gaps in Micro-Electro-Mechanical-Systems (MEMS) gives rise to field emission currents and this is already considered a reliability issue resulting in device degradation and/or failure. This work aspires to offer another perspective with respect to the field emission related phenomena in Radio Frequency (RF)-MEMS, focusing the attention prior to the failure and emphasizing on a reliability aspect affecting the signal integrity. This stems from the non-linear nature of the field emission currents and instigated during their simultaneous presence with RF signals, particularly of high power. Theoretical calculations reveal that this combination results in the generation of new harmonics in addition to the stimulated one. This effect dependents on the distortion induced in the field emission current by the simultaneous excitation by both the DC and the RF biases. Apart from the applied biases, additional parameters contributing indirectly, such as the operation frequency and the device characteristics are having a major role. These outcomes should therefore be considered when designing (high-power) RF MEMS applications.