Spain, in general, has a low crime rate and Cordoba is no exception.
However, as with any well-known tourist destination, there will be people trying to take advantage of travellers. Pickpockets and scammers are known to operate in and around the city, especially around the big attractions. Do not keep your wallet or phone in your back pocket. Be aware of your surroundings and don’t flash your cash. Only buy tickets from official kiosks and, if you’re unsure about how to do that, check online about the attraction before you go.