To check your data balance on Airtel Nigeria, you can use one of the following methods:

1. USSD Code: Dial *140# on your Airtel line and wait for a few seconds. You will receive a message displaying your data balance and its validity.
2. SMS: Send an SMS with the keyword “BAL” to 141. Airtel will respond with a message containing your data balance and its validity.
3. Airtel mobile app: Download and install the Airtel mobile app from your device’s app store. Log in with your Airtel phone number and navigate to the “Account Information” section. You will find your data balance displayed there.

Remember to ensure that you have an active internet connection before attempting any of these methods.