The brainstem locus coeruleus (LC) influences a broad range of brain processes and is suspected to be involved in many neurological disorders. The LC contrast is an accepted marker of the integrity and can be assessed with specific Magnetic Resonance Imaging (MRI) structural sequences. The small size of the LC has rendered its functional characterization difficult. A full characterization of the LC in healthy young and late middle-aged individuals is needed to determine to potential roles of the LC in different medical conditions. Here, we wanted to determine whether the activation of the LC in a mismatch negativity task changes in aging and whether the LC functional response was associated to the LC contrast. We used Ultra-High Field (UHF) 7-Tesla functional MRI (fMRI) during an auditory oddball task in 53 healthy volunteers, including 34 younger (age: 22.15y ± 3.27; 29 women) and 19 late middle-aged (age: 61.05y ± 5.3; 14 women) individuals. Whole-brain analyses confirmed brain responses in the typical regions previously associated with mismatch negativity. When focusing on the brainstem, we found a significant response in the rostral part of the LC (and most extensively in the left LC). Individual LC activity was not significantly different between young and late middle-aged individuals. Critically, while the LC contrast was higher in older individuals, the functional response of the LC was not associated with its contrast. These findings show that the age-related alterations of the LC structural integrity may not necessarily be related to changes in its functional response.