Older adults process and remember positive information relatively better than negative information, compared with younger adults; this is known as the positivity effect. This study examined whether older adults compared with younger adults also respond differently to positively and negatively framed questionnaire items. Participants (N = 275; age = 18–81 years) were randomly assigned to a positively or negatively framed version of a self-efficacy for physical activity questionnaire. Self-efficacy, physical activity intentions, and planned physical activity in the following week were regressed on experimental group and age, controlling for baseline physical activity and covariates. A significant Age × Frame interaction showed that item framing made a difference in planned physical activity for the oldest age group (+350 min compared with the youngest group). This study provides initial support for the positivity effect in item framing on physical activity plans, but not on intentions or self-efficacy. Item framing should be taken into consideration for accurate measurement, but could also be a simple intervention approach.