Activity of animals is influenced by ambient temperature and increasing temperatures brought about by climate change may impose a heat stress risk. Previous studies investigating the effect of heat waves on activity usually measure animals at different, but constant temperatures, however, rarely are they studied under a natural temperature cycle. General activity, behavioural flexibility and frequency of water drinking counts during a normal day, hot day and a simulated heat wave temperature cycle were studied in the crepuscular four-striped field mouse, Rhabdomys dilectus, and the nocturnal Namaqua rock mouse, Micaelamys namaquensis. Both R. dilectus and M. namaquensis showed typical daily locomotor activity under control conditions. During the heat wave, peak activity times changed for R. dilectus, but both species exhibited higher bouts of activity for the heat wave during the day compared to the control, which was accompanied by an increased amount of time spent drinking water. The increased activity during the heat wave is likely due to enhanced water requirements and potentially a form of behavioural thermoregulation as animals may be uncomfortable and try to move to cooler areas. Thus, in the absence of a typical microclimate, access to water may allow rodents to overcome heat stress from extreme temperatures without having to shift their temporal active times.