Rodents are integral components of ecosystems as they provide several important ecosystem services. Despite their importance as prey, pollinators and seed distributors, African rodents are largely understudied. The effect of anthropogenic changes such as artificial light at night extend past urban areas to peri-urban and rural habitats and can have profound effects on entire ecosystems. We investigated the effect of dim light at night (dLAN) on the locomotor activity rhythms of the African pygmy mouse (Mus minutoides). Pygmy mice showed a dramatic, intensity dependent reduction in their locomotor activity when subjected to dLAN, which was accompanied by a delay in the activity onset. We also considered masking responses with a dark pulse during the day and a light pulse at night. All animals became inactive in response to a light pulse during the night, whereas approximately half of the animals showed activity during a dark pulse in the day. Our results suggest that the African pygmy mouse is highly sensitive to light and that their activity is strongly masked by light. In their natural environment, vegetation could shield pygmy mice against high light levels, however other anthropogenic disturbances can affect the behaviour of these animals and could affect their survival.