Trojan.Agent refers to a generic Trojan malware detection. It is used for detections that are either associated with no specific malware families or not enough information is available to pinpoint the malware family.
This is a generic detection for a family of backdoors that can download and install other malware on the infected system.
Malwarebytes can remove this threat without further user interaction. However, it is recommended to do a full system scan since this backdoor may have been used to install more malware onto the system.