Yes, oxygen can be created aboard the ISS using either oxygen generators, pressurized oxygen tanks or solid fuel oxygen generators (oxygen candles). The first method creates oxygen using electrolysis, as a result of which water gets split into hydrogen and oxygen gas. The former is released into space, while the latter is circulated within the cabin.
The second method entails delivery of oxygen from Earth. When supply ships, automated transfer vehicles or the space shuttle docks at the ISS, oxygen is pumped into pressurized tanks, which is then circulated inside the cabin.
The third method relies on chemical reactions that break down sodium chlorate into sodium chloride and oxygen gas.