That seems to be a NetGear log entry, there are two possibilities for this:
SYN Port Scan: Someone (very likely automated, by an infected machine) attempting to scan your machine. They send a SYN packet to you, then your machine responds with an ACK packet. In order to prevent a connection from being established, they send you an RST (Reset) packet. (More likely)
DoS Attack: Someone (again, very likely an infected machine) attempting to flood you with RST packets. (Less likely)
In both cases, your router's internal firewall is responding by dropping those packets. You don't need to worry about that at all. You're on the Internet, something will always attempt to attack you.
And just to be sure, I've checked the IP address bothering you, it seems to be blacklisted for
Portscans or hacking attempts were seen against an UCEPROTECT-System
Update: Just to keep the information up to date, I'd like to mention that the IP address is no longer blacklisted, which suggests that the infection is likely to have been cleaned.