Federica Mogherini is leading a delegation of seven EU commissioners for the discussions, which follow on from last year's historic nuclear deal with the Islamic Republic.
Her visit also marks the start of a new phase in relations.
Trade, energy and the environment are areas both sides are keen to explore.
The BBC's Chief International Correspondent Lyse Doucet, who is travelling with the EU delegation, says that the signing of the nuclear deal paved the way for the lifting of financial sanctions against Iran.
At the same time Iranian President Hassan Rouhani has held talks with Turkey's President Recep Tayyip Erdogan in the presidential palace in Ankara.
They are reported to have discussed the Syrian conflict and strengthening trade links which they hope will rise to $30bn within two years.