Shares in the company more than halved in April when Imagination said that Apple was to stop using its technology.
The US company uses the UK firm's chip technology in its iPhones, iPads, and iPods under a licensing agreement.
Imagination said it had received interest from suitors in recent weeks so had begun a formal sale process.
It added it was now in preliminary talks with potential bidders.
In April, Imagination said that Apple, which accounts for about half of Imagination's revenues, was planning to stop using its technology within "15 months to two years".
At the time, it questioned whether Apple would be able to develop its own computer chip designs without breaching Imagination's patents.
Last month, Imagination announced it had started a dispute resolution procedure with Apple over licensing payments.
In its latest update, the company said it remained "in dispute" with Apple.
Separately, Imagination said the sale process for its MIPS and Ensigma businesses - which was announced in May - was "progressing well", with indicative proposals received for both units.
News of the sale sent shares in Imagination up 15% in early trade to 142p. However, the share price still remains nearly 50% below the level it was at before Imagination announced it was being dropped by Apple.
UK chip designer Imagination Technologies - which is in dispute with Apple, its largest customer - has put itself up for sale.