In order to accurately interpret the image data of NSOM instruments, it is important to fully understand the near-field optical phenomena involving the electromagnetic scattering characteristics of sample objects illuminated within the near-field of a subwavelength aperture. To this end, a finite-difference time-domain (FDTD) model was derived and implemented according to the physical attributes of an NSOM instrument. Specifically, the NSOM instrument was modeled as a subwavelength aperture located within an infinite PEC plane which was then illuminated by an incident plane wave. Absorbing boundary conditions were then utilized to simulate the free space surroundings of the instrument. Furthermore, a near-field to far-field transformation was required to simulate radiation incident upon a detector located in the far-field. Once the basic model is implemented, it can then be utilized to simulate various samples of interest including thin PEC wires, PEC plates, and dielectric slabs. For example, thin PEC wire samples can be compared to closely spaced PEC plates. In this manner, it is possible to gain a better understanding of NSOM effects such as polarization, aperture/sample separation distance, and aperture size.