Humanoid social assistive robotics (SARs) can promote activity engagement for older adults living with dementia. Few studies, however, evaluate the capacity of humanoid SARs to encourage activity engagement in long-term aged care facilities (LACFs). The complexity of the environment, robot design, and personal attributes underscore the challenge of humanoid SARs to encourage activity engagement in practice. This study employed a mixed-methods approach involving nine participants (aged ≥65 years) with mild to moderate cognitive impairment from one aged care facility and seven carers from four different Australian states. Through the triangulation of observational engagement data, participants’ semi-structured interviews, and carers focus group discussion, six themes encompassing activity engagement were identified and are discussed for future application and evaluation of humanoid SARs in dementia care: (1) robot physical design, (2) interaction patterns, (3) activity guidelines, (4) intervention environment, (5) personal history, and (6) relationship establishment.