A woman, 70, died after being struck by lightning while working outside in Golestan province, the website of state television channel IRIB said.
Three others -- two parents and their child -- drowned in flash floods near a burst river bank, it added.
Storms swept across provinces in the north and northwest yesterday and the inclement weather continued into today.
"Severe storms have greatly damaged more than 900 houses in the city and villages and 100 workshops in Amol," official IRNA news agency quoted local governor Ahmad Monfared as saying.
Officials have warned that the storms could reach the northeastern Khorasan Razavi province by later today, Mizan added.
Roads were blocked in some Golestan areas, leaving motorists stranded, a local crisis management official told Mizan.