Interest in the implicit processing of activity behaviors has been growing, but the psychometric properties of its measurement are often overlooked. This study examined the reliability and validity of two implicit association tests (IATs) designed to assess implicit affective and motivational processes. In the first session, 101 college students completed a Liking-IAT, a Wanting-IAT, and a survey on their attitudes and intentions regarding physical activity and sedentary screen-based recreational activities. One week later, participants reported their engagement in these activities, and 34 of them completed the IATs again. The psychometric evaluation revealed high split-half correlation coefficients and significant correlations with behavioral attitudes and intentions for both the IATs, indicating good split-half reliability and convergent validity. The Liking IAT but not the Wanting IAT demonstrated satisfactory test-retest reliability over a one-week interval and predictive potential for weekend physical activity and screen time. Divergence in psychometric performances suggests underlying differences in corresponding implicit processes, highlighting the need for further investigation into the temporal validity, sensitivity to change, and the interplay of various implicit processes.