The shares of Facebook Inc (NASDAQ:FB - 21.28) are headed higher in afternoon trading. However, it looks like some options traders are gambling on some short-term volatility for the social networking concern, as evidenced by today's appetite for weekly option contracts.

Specifically, traders are flocking to FB's weekly 21.50 strike, which has seen roughly 8,300 calls and 5,800 puts change hands. The majority of the contracts have crossed the tape at the ask price, and volume has exceeded open interest on both sides of the aisle, pointing to buy-to-open activity.

By purchasing the calls to open, the buyers are expecting FB to muscle atop the $21.50 level by the end of the week, when the weekly options expire. In fact, the volume-weighted average price (VWAP) of the calls is $0.36, meaning the buyers will reap a reward if FB conquers the $21.86 level (strike plus average premium paid) by Friday's closing bell. On the flip side, the VWAP of the puts is $0.56, indicating a breakeven level of $20.94 (strike minus average premium paid) for the buyers.

Technically speaking, the shares of FB have outperformed the broader S&P 500 Index (SPX) by more than 13 percentage points during the past 40 sessions. Nevertheless, the options crowd remains wary of the stock. The security's Schaeffer's put/call open interest ratio (SOIR) sits at 1.45, indicating that puts outnumber calls among options with a shelf-life of three months or less. Plus, the equity's 10-day put/call volume ratio on the International Securities Exchange (ISE), Chicago Board Options Exchange (CBOE), and NASDAQ OMX PHLX (PHLX) stands at 1.29, suggesting option buyers have initiated more bearish bets than bullish during the past couple of weeks.

In the front-month series, the November 20 strike is most popular, with more than 3,100 puts outstanding. In the short term, this glut of pessimistic positions could translate into an options-related foothold for FB.