The research presented in this paper concerned the effects of activation level on the short-term memory (STM) scanning. It was assumed that the efficiency of STM scanning would vary between participants with low and those with high momentary activation (energetic arousal and tense arousal) as well as between participants manifesting low indices versus those with high indices of constitutional arousal (PEN range of extraversion/introversion and neuroticism). The tested individuals (N=70) were participant to the computerized memory TURBO Sternberg's test twice. Their task was to memorize a successively presented set of digits and then to ascertain whether a separately presented control digit belonged to the previously shown set of stimuli. A relationship was noticed between extraversion and the efficiency of STM scanning. Also some relationships between momentary activation and efficiency of short-term memory were observed. These results suggested the existence of multiple sources of activation determinants in cognitive functioning and their reciprocally modifying effect on selected sub-factors of the cognitive system.