Similar to other executive functions, inhibitory control is thought to be a dynamic process that can be influenced by variations in task difficulty. However, little is known about how different task parameters alter inhibitory performance and processing as a task becomes more difficult. The aim of this study was to investigate the influence of varying task difficulty, via manipulation of reaction time deadline (RTD), on measures of inhibitory control, perceived effort, and task-related arousal (indexed by skin conductance level). Sixty adults completed a visual Go/Nogo task (70% Go) after being randomly assigned to one of three task difficulty conditions: High, Medium and Low, with RTDs of 300, 500 or 1000 ms, respectively. Results revealed incremental increases in Go/Nogo errors and greater perceived effort with increasing difficulty. No condition differences were found for arousal, but the amplitude of the Nogo N2 increased and peaked earlier with increasing task difficulty. In contrast, the Nogo P3 effect was reduced in the High condition compared to the Low and Medium conditions. Finally, the amplitude of N1 and P2 showed differential effects, with Nogo N1 increasing with task difficulty, while the Nogo P2 decreased. This study provides valuable baseline behavioural and ERP data for appropriately manipulating difficulty (via RTD) in Go/Nogo tasks — highlighting the potential key role of not only the N2 and P3, but also the N1 and P2 components for task performance.