No, it’s normal if you have more than one gateway around (every gateway will receive your signal, including those not in TTN but in other networks). The network is able to deal with this (deduplication etc. ). (EDIT - written while @BoRRoZ posted )
If you own the gateways, do not place them too close to each other
LoRaWAN is not WiFi where a client connects to a gateway, LoRaWAN packets are received by all gateways within radio coverage and forwarded to the back-ends of those gateways. (There may be commercial operator and private LoRaWAN networks receiving the same data)
In the back-ends of the networks the data will be verified using the secret keys and if a packet is found to be valid it will be routed to the defined end-point for that application.