What is the ruling on wearing hijab in Ramadan only?

Hijab is obligatory in Islamic law. This implies that it is obligatory for Muslim women to wear hijab during that blessed month and at other times.

Repentance and Ramadan
Ramadan is the month when Muslims are expected to increase their tawbah [repentance], turn over a new leaf as well as make it the starting point for doing righteous deeds that will guide them to Allah Almighty and ultimately gain His pleasure.

The Ruling
A Muslim, who is granted success in worshiping Allah Almighty and obeying His commands in the month of Ramadan, must continue in the same path after Ramadan. This is because success in observing good deeds is a sign of having them accepted.