Previous findings indicate that the way words are organized in the mental lexicon may differ in Arabic and English. While words are organized according to both orthographic and morphological form similarity in English, they are organized primarily according to morphological form similarity in Semitic languages (Frost et al. in J Exp Psychol Learn Mem Cogn 23:829-856, 1997; J Exp Psychol Learn Mem Cogn 31:1293-1326, 2005). The purpose of this study was to determine whether L1 English learners of L2 Arabic organize their L2 mental lexicon so that they show nativelike patterns of lexical activation, and whether this depends on proficiency level. Native speakers of Arabic, intermediate-proficiency, and advanced-proficiency learners completed a masked priming, lexical decision task in Arabic. Response times were measured to target words preceded by primes that were orthographically or morphologically related, identical, or unrelated. Results showed that native speakers and L2 learners patterned alike regardless of proficiency level.