The paper presents findings of an experiment the participants of which were native Czech speakers (L1 ) possessed of perfect knowledge of English (L2). We assumed that the subjects could process differently each of the three types of English and Czech sentences; the first type represented correct sentences, the other two violated sentences. Violated sentences differed in the precise relationship between the verbs, their preceding noun phrases, and their preceding context. ERPs to critical verbs, the accuracy rate for both English and Czech sentences processing and decision time for each were evaluated. Participants' personality traits were assessed too. It has been shown that our subjects, who learned English after the age of 15, displayed significant differences in all measured parameters. It was especially the longer latency N400, the lower accuracy rate of English sentence processing, the longer decision time, and the same dynamics of all measured ERPs parameters. Possible causes of these differences are discussed.