Ms Mogherini is keen to discuss the nuclear situation in Iran but appears less inclined to support protestors.
The US president declared in October that the agreement was "one of the worst and most one-sided transactions the United States has ever entered into", and warned that within a few years Iran would be able to "sprint towards a rapid nuclear weapons breakout".
The Associated Press cited unnamed administration officials saying lawmakers had made progress in amending U.S. legislation that governs Washington's participation in the landmark agreement, allowing Trump to extend relief from economic sanctions to Tehran. He took the same action in October in the last round of waivers, passing the decision on whether to impose additional sanctions on Iran to Congress.
The State Department has said an announcement on the sanctions waivers would be made Friday.
Mr Johnson described the deal, which is known formally as the Joint Comprehensive Plan of Action (JCPOA), as a "considerable diplomatic accomplishment". Various members of Congress and US allies, including Israel, have said that as restrictions against Tehran are lifted under the deal, Iran's "breakout" window will shorten dramatically.
European firms have moved quickly to reestablish business ties after the nuclear deal. Trump also attacked the deal for shipping $400 million in currencies representing assets frozen by this country in the wake of the 1980 crisis, in which Muslim extremists took over the American embassy in Tehran and held 52 US nationals hostage for more than 400 days.
This opened the door for the resumption of USA sanctions against Iran.
Obama-era officials sent mixed messages on the deal when it was being negotiated.
One of the criticisms levelled at the nuclear deal is that it does nothing to address Iran's continuing ballistic missile program and involvement in conflicts such as Yemen and Syria. Any of these changes, however, would have to get significant support among Republicans and Democrats in Congress.
The European signatories of the Iran nuclear deal have warned Donald Trump from ditching the accord, arguing that it is essential to maintain worldwide security and is achieving its goals.
Despite being outspoken in his criticism of USA foreign policy since President Donald Trump took office a year ago, Gabriel has also said the United States was right to address concerns about Iran's strategy in the Middle East.
Iranian state broadcaster IRIB quoted Zarif as saying that in light of "U.S. destructive policies", the Brussels talks will focus on the nuclear deal, not on antigovernment street protests that have rocked Iran in the past two weeks and claimed at least 22 lives.