Cognitive-motor interference has been investigated for both, the influence of balance control demands on performance in cognitive tasks and for the influence of cognitive task demands on balance control. Traditional approaches, using posturography aggregated balance control measures over relatively long time periods (e.g., minutes), do not differentiate the role of specific cognitive processes at the balance level. Recent studies using an event-related methodology found that response conflict (i.e., the congruency effect in a Simon task) in a concurrent reaction time task lead to reduced short-term variability of balance control. Here, we combined a balance task with a cognitive dual-task paradigm. This dual task consisted of a visual short-term memory task requiring a deferred verbal response and an auditory-manual reaction (RT) task, with variable stimulus-onset asynchrony (SOA). With short SOA, we found longer RT (“response bottleneck” effect) and increased variability in the balance control domain. Moreover, compared to single-task conditions (RT task without memory task), we also found longer RT (dual-task effect) and increased balance control variability in the dual task. We assume that manual response postponement (SOA effect) and the general costs of maintaining more than one task set may lower the accuracy balance control, such overshooting an intended balance state. In contrast, reduced sway variability by response conflict in the Simon task (congruency effect) suggests that code-specific response crosstalk may briefly suppresses balance control as the consequence of a balance control “micro-bottleneck”. Using the current event-related approach can help to better specify the cognitive-motor interference effects in balance control.