The generation of low-frequency radiation at around the terahertz frequency, caused by a linearly polarized intense laser pulse passing through a low-density homogeneous plasma, is studied by one-dimensional particle simulations. The excited transverse current component with its frequency at the electron plasma frequency serves as a radiation source to generate electromagnetic waves both in the front and the rear side vacuum regions of the plasma layer. It is found that the electromagnetic radiation fields increase with both increasing plasma density and increasing laser amplitude.