This study is an investigation of the validity of the Online Test Anxiety Inventory (O?-TAI) for adult students. The scale contained the 20 items of the Test Anxiety Inventory (Spielberger, 1980), together with five computer anxiety items, all rephrased so as to pertain to online test anxiety. The scale was administered to a large sample of Greek and Cypriot postgraduate students and Rasch measurement was used for the investigation of its psychometric properties. After original analyses, one of the computer anxiety items was removed, leaving the final instrument with a total of 24 items. Results showed that the scale is unidimensional thus supporting that computer anxiety can indeed be considered a component of online test anxiety. All evidence collected supports the high degree of construct validity of the scale. Furthermore, results verify that the 4-point scale used is optimal. Additional research, with adult student populations from other countries, with the use of the O?-TAI is suggested for the purpose of broader use.