Behavioral flexibility is attributable to the changes underlying neural connectivity in the brain. However, it is not clear how the cortical network is dynamically modulated in behaving animals. Recently, it is hypothesized that cortical oscillations contribute to regulate the functional connectivity and the oscillations are modulated by the lateral prefrontal cortex (lPFC). lPFC is known to have anatomical connections between many cognitive- and motor-related areas, and thought to play crucial roles in altering the functional connectivity. Here we examine the task-dependent modulation of local field potentials (LFPs) recorded from the lPFC while monkeys were performing a shape-manipulation task that required them to plan step-by-step movements based on memorized information of shapes. We conducted time frequency analysis to investigate how the cortical oscillations are involved in flexible planning of actions and execution of the sequential movements. This study would reveal the functional roles of the PFC in performing behavioral tasks by altering the cortical oscillations.