Octopuses function as important prey and predators in many continental-shelf marine ecosystems. Understanding activity cycles of octopuses should help define their mode of foraging and potential resource utilization and, therefore, their niche within the marine community. Unfortunately, little is known concerning activity cycles of octopuses, especially during their juvenile life-history stages. Here, I present observations on juvenile activity in Octopus bimaculoides Pickford and McConnaughey, 1949 over three observational weeks in a semi-natural laboratory setting. Octopuses on average were nocturnal, but some individuals were active during daylight hours in all three observational weeks. Nocturnal activity cycles may decrease the risk of predation on juveniles by visual fish predators hunting during daylight hours. However, inter-and intraspecific competition with other octopuses in different life history stages, including adult O. bimaculoides and adult and juvenile Octopus bimaculatus Verrill, 1883 is also likely during nighttime hours. Further studies are needed on the relative influence of predation and competition on octopus activity cycles and the resulting consequences for octopus populations.