To assess the effect of the aroma of the essential oil of Roman chamomile (Chamaemelum nobile) and the impact of induced expectancy on mood and cognition in healthy adults, 80 volunteers participated in an independent groups design study. There were four conditions: (1) aroma and arousal expectancy, (2) aroma and sedation expectancy, (3) aroma and no expectancy, and (4) no aroma controls. Expectancy effects were induced by means of a pre-test session where participants were provided with false information from a supposed official source. Pre-test mood scales were completed followed by the Cognitive Drug Research (CDR) battery and a final post-test mood scale. Analysis revealed a significant effect of condition on overall quality of memory (p = 0.017), long-term memory (p = 0.008) and accuracy of attention (p = 0.024). Analysis of the pre to post-test changes in mood revealed significant changes in alertness (p = 0.002), and calmness (p = 0.00004). The sedative nature of the aroma appeared to combine with induced sedative expectancy to impair cognitive performance to a greater degree than was found for aroma alone. Subjective alertness was influenced by the sedative effect of the aroma which was ameliorated to some degree by the induced arousal expectancy. Similarly, subjective calmness appeared to be influenced by both the sedative effect of the aroma and induced arousal expectancy.