Carlos Queiroz's side have not tasted victory since a 3-2 FIFA World Cup qualifying win against Kuwait in March and will be eager to end that run before they travel to Brazil.
But they only have one chance to do so now, with their friendly against Trinidad and Tobago on June 7 taking on even more importance.
It could have been worse for Iran, who fell behind three minutes before half-time to Silva's header, but Ansarifard got on the end of Ehsan Hajsafi's ball to slot home in the 56th minute.
Angola edged in front towards the end of the first period, Silva glancing in Gilberto's curling right-wing free-kick at the far post with goalkeeper Daniel Davari rooted to his line.
They were level before the hour mark, however, Ansarifard firing home left-footed from inside the area following Hajsafi's pass.
Neither side was able force a winner in the closing stages, though, and Iran will be keen to return to winning ways before they open their World Cup campaign against Nigeria on June 16.
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