An efficient novel frequency domain finite element approach for the analysis of photonic crystal resonant cavities is presented. This approach uses isoparametric triangular elements for the discretization and perfectly matched layers to limit the computational domain. Besides, it solves a linear system of equations instead of an eigenvalues problem, in this way, less computational effort is needed. The resonant frequency, the field pattern, modal area and the quality factor of the resonant mode of a finite-sized cavity are rigorously calculated.