The study is a full-scale investigation of the presence of the activation of L1 in L2. In order to portray a more holistic picture of Korean L2 learner’s lexical processing, the present study addresses variation in relation to stimuli and tasks both written and oral type in both L2 comprehension and production. The results show the evidence of the activation of non-target language (L1) as a form of Konglish in L2 (English). The factors affecting L1 activation in L2 were proficiency, the quantity and quality of English exposure, Korean-medium learning context. If Korean learners of English are exposed to an L1-inducing learning environment in Korea, they may not be able to develop an adequate lexical network in respect of English. In addition, if their exposure to English is sparse in quantity and of poor quality, thus not providing a very promising basis for the restructuring of their explicit knowledge of English learned through Korean, the activation of non-target language (L1) may be inevitable. Therefore, the development of L2 knowledge in the learner’s mental lexicon, through the quantity and quality of target language exposure and L2-promoting learning process, should be carefully considered in English leaching in Korea.