Can a person from arts background with masters in Computational Linguistics do Masters in Applied Mathematics? I have a bachelor in Linguistics and masters in Computational Linguistics with cgpa 3. After using Machine Learning for my thesis work, I am realizing my interest in Applied Mathematics. I do not know, how to begin. But I plan to take Math sub-gre and also to do a small project in Applied Mathematics with a scientist I know. Given these details, will I be eligible to do a Masters in Applied Mathematics from US/Canada?
You should start by writing to the graduate program directors of the departments where you are considering pursuing an MS in applied math. Explain you background and ask whether you can be considered for admission to their MS programs.

Typically,  master's level courses have one or more undergraduate courses in the same discipline as prerequisites. If you don't have these prerequisites, I am guessing that many universities in the US/Canada would be reluctant to admit you into their graduate programs. However, some departments may have an option where a student without an undergraduate degree in specific field or related fields takes a few essential courses at the undergraduate level (in that specific field) and obtains a minimum specified GPA. The student is then offered admission to the graduate program.