Introduction: The aim of the present study was to use a psychological model to explain the effects of individual differences in trait anxiety and stressful situational on the processing efficiency and working memory performance. It was designed to test Eysenck and Calvo, processing efficiency theory which suggests that anxiety has a greater adverse effect on the processing efficiency than on performance effectiveness.Method: A sample of first year college students ( n = 283) completed the trait measure of the Spielberger State – Trait Anxiety Inventory. After scoring, 48 subject belonging to the .25 percent of upper distribution and 48 subject from the .25 percent of lower distribution were selected. They were then randomly assigned to four groups based on level of anxiety (high / low) and exposure to threat/ non-threat. Measurements of task accuracy were taken as an indicator of performance outcome or effectiveness. Time taken to complete task and a subjective rating of mental effort were taken as measurement of performance efficiency. Data were analyzed using two-way ANOVA.Results: Analyses explored the effect of trait anxiety (high versus low) on mental effort rating. There was significant interaction effect of trait anxiety and experiment conditions on time and accurate responses.Conclusion: The results suggested that the high anxiety group increased their effort in order to maintain levels of performance comparable to the low anxiety group. When the conditions were stressful the high anxiety group was lower performance.