First off, I would like to answer your question. With Google AdWords, you have 3 different keyword match types, which are 1. broad, 2. "phrase" and 2. [exact match]. When you add your keywords to your adgroup, if you aren't using "" or  around your keywords, then you will run into this problem. Here is Google's Exmplanation:
The Google AdWords system automatically runs your ads on relevant
variations of your keywords, including synonyms, singular and plural
forms, possible misspellings, stemmings (such as floor and flooring),
related searches, and other relevant variations. To help deliver
relevant matches, this match type may also take the customer's recent
search activities into account.
With the aforementioned, broad match keywords could very easily cause facebook-related queries to trigger your ad, because "broad match may also take the customer's recent search activities into account." source: support.google.com
You should always have a negative keyword list with any campaigns, after reviewing the keywords which triggered an ad to display, and determining that one or more keywords will not help you reach your objectives. Negative keywords are essential to a successful campaign.
However, If I am going to try and give the best advice, I'm going to suggest that you change your current strategy to either use a website, or even send traffic to a Google+ page. Here are some considerations:
- if you want the user to interact with your page (i.e. like it, share it, or send you a message) you are assuming that they are already logged in. It's self-evident to assume that many users will not be logged-into facebook at the time they click the ad, which is creating an extra step. It's technically even possible that they may not have a facebook page at all.
Hopefully this helps. If you care to share your advertising objective, I could possibly provide better advice. Good luck to you!