Other than the being more expensive than other areas of the UK, car insurance in in Northern Ireland is largely the same as in England, Scotland or Wales.
However, when it comes to picking a policy you may want to consider:
Crossing between Northern Ireland and the Republic of Ireland
Do you live in a bordering county and it's a trip you regularly make? Or maybe you just happen to cross between NI and the Republic occasionally? Either way, you'll want to check whether your chosen policy covers you to drive there.
Some insurers may class the Republic of Ireland as abroad. If that's the case, you may need to look at taking out European car insurance separately for longer trips. Or just check with your prospective insurer how long your standard policy covers you for. Some insurers offer cover to drive in Europe for up to 30 days.
Insurance on car ferries
With ferries from England and Scotland regularly travelling to the ports of Larne and Belfast, it's pretty convenient to visit other parts of the UK.
However, if you plan to use one regularly or even just as a once-off, you'll want to check what level of cover the policy you're looking at includes. Make sure you're protected should you have an accident while you're boarding, on-board or disembarking.
Neither of these points should prevent you from finding insurance. But if they affect you, you'll want to make sure any policy you're looking at does what you need it to. If you're in any doubt, speak to the insurer or check the policy documents before buying.