The agency, owned by Accenture, beat WCRS, TBWA and Mcgarrybowen to the £6m account in June 2016.
Karmarama rolled out a relaunch of the brand in September, involving a visual revamp alongside an ad campaign.
This contrasted with the more light-hearted brand advertising that had characterised its marketing activity from 2014 when Red Brick Road has the brand's ad business.
The current review is being led by UK marketing director Ben Carter. The brand has held chemistry meetings with a number of agencies and is set to create a pitch shortlist.
A Just Eat spokeswoman said: "Following our rebrand in 2016, we've worked closely with Karmarama to increase the appeal of the Just Eat brand and positively reflect the breadth of choice and diverse food options that are on the Just Eat platform nationwide.
"The rebrand and subsequent campaigns have helped to reposition the Just Eat brand while accelerating our business growth.
"In an increasingly dynamic market and with food delivery rapidly becoming the norm, we want to take this opportunity to look at our creative advertising strategy and will be discussing this with our incumbent as well as a small number of other advertising agencies."