How close is the Tysons Corner Metro stop to the shopping mall? Is it within walking distance?

Yes, the directions above are perfecto.

You exit the train, take the elevator/escalator/stairs to the upper level then turn left and walk across the bridge to reach Tyson's Corner Center. For Tyson II, you will need to exit the metro station, turn left and cross the street at the first traffic light. Walk left for a min and there it is!

Yes, its right across the street