Focusing internally on movement control or bodily sensations is frequently shown to disrupt the effectiveness and efficiency of motor control when compared to focusing externally on the outcome of movement. Whilst the behavioural consequences of these attentional strategies are well documented, it is unclear how they are explained at the corticomuscular level. The aim of the present study was to investigate how attentional focus strategies affect kinetic, cortical, muscular, and corticomuscular activity during an isometric force precision task. In a repeated measures design, we measured force, EEG and EMG activity from twenty-seven participants who performed 160 isometric contractions of the right hand whilst encouraged to adopt either an internal or external focus through a combination of instructions, secondary tasks, and self-report evaluations. Results indicated that focusing internally led to poorer force accuracy and steadiness compared to an external focus. An internal focus also increased muscle activity of the forearm flexor, increased EEG alpha activity across the parieto-occipital cortex, lowered frontal midline EEG theta activity, and lowered beta corticomuscular coherence between the forearm flexor and contralateral motor cortex. The results of this study provide a holistic understanding of how attentional focus strategies alter neuromuscular control during an isometric force precision task, paving the way for exploring how the behavioural consequences of attentional strategies can be explained at the corticomuscular levels across a wide range of motor tasks and contexts.