Urgent! Regarding an offer

Now, a small CPA firm want to give me an offer through a recruiter. This is a temporary job, from Jan. to Apr. and the owner wants me to promise her do not look for other jobs.(She knew that I want a permanent job). Should I accept it and keep looking for other job? Can I do that? If I get another offer after I accept this one, can I reject the one? Is there any trouble?

Thanks!