Objective: Numerous studies using dual-task paradigms (postural and cognitive) have shown that postural control requires cognitive resources. However, the influence of postural control on attention components has never been directly addressed. Method: Using the attention network test (ANT), which assesses specifically each of the 3 components of attention—alertness, orientation, and executive control—within a single paradigm, we investigated the effect of postural balance demand on these 3 components. Forty-two participants completed the ANT in 3 postural conditions: (a) supine, a very stable position; (b) sitting on a chair, an intermediate position; and (c) standing with feet lined up heel to toe, a very instable position known as the Romberg position. Results: Our results revealed that the difficulty of postural control does modulate alerting in such a way that it improves with the level of instability of the position. Regarding the orienting and executive control components of attention, performance was not different when participants were standing upright or seated, whereas in the supine position, performance dropped. Conclusions: The strong and specific interaction between postural control and the alerting system suggests that these mechanisms may share parts of the underlying neural circuits. We discuss the possible implication of the locus coeruleus, known to be involved in both postural balance and alerting. Also, our findings concerning orienting and executive control systems suggest that supine posture could have a specific effect on cognitive activities. These effects are discussed in terms of particularities resulting from the supine position.