The only way to know for sure what the cause is related to is to have the vehicle scanned for DTCs (Diagnostic Trouble Codes) in the airbag module. However, a very common problem on these cars is a two-pin yellow connector under the drivers and passengers seats that loosen an internal connection causing an open in the circuit causing the light to come on. The repair is to disconnect the connectors and slightly bend the pins to create a better connection. For example, if the pins were to look like this: I I , you would want to slightly bend them to where they look like this / \. THen reconnecting the connector will secure the connection. Then disconnect and reconnect the battery and start the car. If the light comes back on, you will need to have the airbag module scanned, if not the problem is fixed!
I hope this helps! Let me know if you have any more questions!