This study aims to investigate the most common types of linguistic errors and their frequency occurrence in compositions written by forty (40) non-English major Libyan students at the pre-intermediate level in Language Centre at Omar EL-Mukhtar University, EL-Beida, Libya. A corpus of 40 compositions was collected from a sample of 40 students in order to be investigated in terms of Hubbard et al.’s (1996) taxonomy of errors. This study is designed to answer the following questions: 1) what are the most common types of linguistic errors made in English writing by non-English major Libyan students? 2) How frequent do these errors occur in their English written work? The findings showed that substance errors (331) constituted the highest number of errors, followed by grammatical errors (150), syntactic errors (54), and lexical errors (29). The findings also revealed that spelling, capitalization, tenses, punctuation, articles, varied words, subject-verb agreement, and prepositions were the most common types of linguistic errors found in the students’ writings. These errors could be due to overgeneralisation in the target language, resulting from ignorance of rule restriction and incomplete application of rules and interference resulting from first language (Arabic) negative transfer. This study is important for teachers and educators who should become aware of the types of linguistic errors that their target learners make. These findings are discussed with implications for English as foreign language Libyan teachers. Along with the discussion of findings, limitations of the present study are discussed, and directions for further research are highlighted.