mrt.exe is the process for Microsoft Windows Malicious Software Removal Tool which helps to secure your PC by removing spyware and other unwanted processes.
Microsoft Windows Malicious Software Removal Tool checks your machine for infection by specific, prevalent malicious software including Blaster, Sasser, and Mydoom. The objective of this tool is to remove the infection if it is found. Microsoft will release an updated version of this tool on the second Tuesday of each month. This tool can be downloaded as an update (kb890830)
The process mrt.exe is important for safe and secure Internet browsing and should not be terminated. MRT.exe is located in the folder C:\Windows\System32 and please note that If you find MRT.exe somewhere else other than C:\Windows\system32, then it is probably a malware application.
Non-system processes like mrt.exe originate from software you installed on your system. Since most applications store data on your hard disk and in your system's registry, it is likely that your computer has suffered fragmentation and accumulated invalid entries which can affect your PC's performance.

In Windows Task Manager, you can see what CPU, memory, disk and network utilization is causing the Malicious Software Removal Tool. process. To access the Task Manager, hold down the Ctrl + Shift + Esc keys at the same time. These three buttons are located on the far left of your keyboard.

This process is considered safe. It is unlikely to pose any harm to your system. The mrt.exe file should be located in the folder C:\Windows\System32. Otherwise it could be a Trojan.

This process is not considered CPU intensive. However, running too many processes on your system may affect your PC’s performance. To reduce system overload, you can use the Microsoft System Configuration Utility (MSConfig) or the Windows Task Manager to manually find and disable processes that launch upon start-up.

Use the Windows Resource Monitor to find out which processes and applications write/read the most on the hard drive, send the most data to the Internet, or use the most memory. To access the Resource Monitor, press the key combination Windows key + R and then enter 'resmon'.