It said the review was needed to establish whether certain energy transmission projects were still needed and required funding.
"Following our consultation in November, Ofgem has today decided to launch a mid-period review into the 2013-2021 price controls which will be limited to National Grid Electricity Transmission and National Grid Gas Transmission," Ofgem said on Thursday.
Ofgem said since the review was targeted to a few projects it would not be re-opening the whole price control package.
"Ofgem's mid-period review announcement this morning should not concern investors, as it is focussed on reviewing 3 specific projects in Transmission," analysts at Bernsteil said in a research note.
"It is not a re-opening of the price control to change crucial aspects such as the allowed cost of capital," they added.
Gas and electricity network operator National Grid made 2.9 billion pounds $4.5 billion in pretax profit in the financial year ending March 31 2015.