It is not really related to scope creep with the exception that they're both creeps and they both negatively affect the project.
Effort creep is when one of your team members makes a huge effort on a task that is nearly done, but cannot finish it. For example, a task is 80% done in one week, and the team member is working on the remaining 20% for several weeks, with no end in sight. This is very common in software projects, and the perfect remedy for effort creep is to assign the remainder of the task to someone else who has more experience in the particular area of the task.
Alternatively, the project manager can talk to the team member about the difficulties facing him while working on this task, although this is normally useless, as the reason is always related to the team member's inexperience and inadequacy for the task, and most team members are reluctant to admit it.