People living with dementia (PLWD) and their family caregivers report higher rates of having a sedentary lifestyle than their non-disabled peers do. This study analyzed the effectiveness of an intervention designed to increase physical activity among PLWD and their family caregivers in primary health care settings. A cluster-randomized multicenter clinical trial was conducted. Participants from four health centers were randomly assigned to the intervention group (IG) or the control group (CG) in a 1:1 ratio using Epidat software. After a seven-day period with a digital pedometer (Omron Hj-321 lay-UPS), participants were asked to complete the International Physical Activity Questionnaire Short Form (IPAQ-SF). PLWD and caregivers allocated to the IG were given brief advice, educational materials and an additional 15 min appointment to prescribe an individualized physical activity plan. Seventy PLWD and 80 caregivers were assigned to the CG and 70 PLWD and 96 caregivers were assigned to the IG. Results of the pedometer assessment show that in PLWD, the IG’s activity increased by 52.89 aerobic steps at 6 months and the CG’s activity decreased by 615.93 aerobic steps, showing a net increase in the IG of 668.82 (95% CI: −444.27 to 1781.91;p= 0.227). For caregivers in the IG, activity increased by 356.91 aerobic steps and in the CG it decreased by 12.95 aerobic steps, showing a net increase in favor of the IG of 369.86 (95%CI: −659.33 to 1399.05;p= 0.476). The effectiveness of interventions to increase physical activity in this group of people with dementia and their caregivers did not achieved positive results overall but may have provided suggestions for family physicians and physical therapists to improve physical activity among people with dementia and their families.