Unfortunately attackers scan the internet and are looking for vulnerable systems which they can exploit and then misuse to attack other systems - see for example this information about the VPNFilter botnet exploiting routers or this information about the Satori botnet infecting routers.
Thus, it is very likely that somebody is trying to attack your system. There is nothing you can do against somebody trying to attack you, but you can do something to make sure that the attacker does not succeed. This means especially to not use a router with known vulnerabilities or backdoors, with known default passwords or with weak passwords.
There are several information at this site which can help you with securing your router, for example Best practice for home router configuration, How to recommend a (more) secure router, Are consumer-grade routers any more or less vulnerable? or How to secure a router/modem?.