The current study is an attempt to investigate whether learners perform differently on paper or on the computer in the International English Language Testing System (IELTS) writing test, in terms of Task response/achievement, coherence/cohesion, lexical resource, grammatical range and accuracy. In addition, it explores whether the candidates’ computer familiarity are different in paper or computer groups. To this end, a total number of 108 candidates were selected out of 144 based on the results of the Oxford Placement Test (OPT) in Tehran University, Iran. To gather the data, a retired IELTS academic writing sample and a computer familiarity questionnaire were administered. The participants were divided into two equal groups. In the Paper Mode (PM) group, students were given the test to write conventionally on paper. In the other, Computer Mode (CM) group, the students were given the same test; but were asked to type the test in the computer provided for them in their class. Also, all the participants took the computer familiarity questionnaire. The gathered data were analyzed through the Independent samples t-test. The findings reveal significant differences between paper-based and computer-based modes in both writing tasks. Moreover, the analysis of the questionnaire shows the impact of the candidates’ computer familiarity on their writing performance.