Wii Balance Board vs. Active App: No Hardware Required for Active

You do not need a Wii Balance Board for "Active."

Clarification

• Active (App): A mobile fitness app (iOS/Android) that uses your phone's camera (computer vision) for body tracking. No external hardware.
• Wii Fit / Wii Fit Plus / Wii Fit U: Nintendo Wii/Wii U games that require the Wii Balance Board (pressure-sensitive platform) for weight/balance measurement.
• EA Sports Active / Active 2 (Wii/PS3): Used Wii Remote + Nunchuk (leg strap pouch) for motion tracking; optional Balance Board support for some exercises.

Summary

If you have the Balance Board, you can use it with Wii Fit or EA Sports Active (Wii), but it is irrelevant to the mobile "Active" app.