Will my undergrad thesis be considered for my Master's admission given that my areas of interest has changed a bit?
It’s fairly widely understood that people’s research interests can evolve over time, particularly in the transition from undergraduate to graduate. So, yes, the committee will consider your undergrad paper, precisely because it shows potential for research, even if it’s not in the field you want to study in the graduate program.

You should, however, be sure to make an affirmative argument for your new field of study in your statement of purpose: talk about why you’re gravitating toward the new field, not away from the old one.