Yes. Fish produce waste which is ammonia. Ammonia is transformed into nitrite and nitrite is transformed into nitrate. If you have nitrite and nitrate present, then the tank is cycling. You will need to do daily (or as needed) water changes to lower the levels until the tank finishes cycling. Naturally, you want the ammonia and nitrite to be 0 and the nitrate to be below 60 to 80 but for now, try to keep the ammonia and nitrite below 1 (or below .5 is better).
What size tank do you have, how long has it been running with fish and what fish do you have in it? What are your actual readings for ammonia, nitrite and nitrate?